Practical everyday DFM guidelines: They truly save time and money Part 3: Material, Assemblies, Tooling and Tolerancing

This Blog has spent a lot time talking about the philosophy of Design for Manufacturability (DFM). There are several good books on the subject of DFM and the reader can find in Amazon.com. Just type DFM in the search gadget.  We will nonetheless look at some of the very basic Guidelines to DFM, more specifically at Mechanical / Structural and System design guidelines that I picked up in Design For Manufacturability from David M. Anderson as well as other site on the internet. Part 3, we're looking at Selecting Material which requires some serious considerations. Regardless of the industry, Raw Material account for about 30% of the total cost of a component. We'll be also looking at assemblies, Tooling and finally Dimensioning and tolerancing.

Materials

M1: Number of parts that will be fabricated

Part volume can drive the selection of material format, as well as the transformation process.

M2: Availability of the material

Exotic materials are expensive and create delivery problems and are likely to have a minimum buy clause attached. Common raw materials are generally available and delivered within 24 hrs.

M3: Make from

Can existing parts be used as raw material and modified to suit the need? This will save time in design and minimize inventory.

M4: Corrosion

What are the environmental conditions? Are you dealing with dissimilar materials that can generate galvanic corrosion?

M5: Stress  

Vibration, creep, fatigue, strength, cracking, etc… The Stress-man always has the final word, but you need to understand the reasoning behind the selection.

M6: Toxicity

Some materials generate toxic fumes when processed, i.e. beryllium copper.

M7: Dimensional Stability

Dimensions can be affected by temperature change, humidity levels, etc.: e.g. wood expands under humidity, Stainless steel warps when welded, etc...

M8: Transformation Process

Machinability, weldability, Formability, e.g.: Some aluminum alloy cannot be welded; Stainless Steel has poor Machinability, etc...

M9: Surface Protective Finish

Can it be avoided? Some metals do not require protection. Stainless steel can replace a painted carbon steel part, and will save the costs associated with painting parts.

M10: Environmental

Chemical transformation processes are harmful to the environment. Think green when you select a material or when specifying a Chemical process; Chem-Milling is very bad in every way.

M11: The Design process

Raw material selection is done at the Design Process level, therefore should be defined as early as possible, and should be kept as much as possible to what is stock or easily available. Designers are solely responsible for material selection, and indirectly define the manufacturing process by design. This is the main reason why manufacturing and Material Management need to be involved early in the design process in order to design manufacturing and material management into the product. This exercise will also help defining a preferred raw material list.

Assemblies

A1: Eliminate over-constraints to minimize tolerance demand

The single most expensive factor in product manufacturing is the tolerances generated by over-constraints. See Figure 1.

Figure 1

 A2: Provide unobstructed access for parts and tools

Each part must be designed to fit in its required location, but also must have an assembly path for entry or removal, as well as access to tools. See Figure 2.

Figure 2

 A3: Structure the product into sub-assemblies as appropriate

 The use of sub-assemblies can streamline manufacturing as sub-assemblies can be built and tested separately. More and more Aircraft manufacturers outsource sub-assemblies to partners. The sub-assemblies are later integrated into the assembly line.

A4: Make insertion of components easy

Avoid having components so small that finger grasp is difficult (refer to Guideline SP7) and become difficult to locate as fingers hide assembly location.

 A5: Purchase modules and sub-assemblies assembled and tested

This will eliminate performing incoming inspection, provides quicker feedback to the supplier and allow for repair where the sub-assemblies were built. Modules are typically interchangeable. See Figure 3. These modules are generally purchased via the use of Source Control Dataset (SOCD) or Vendor Item Control Dataset (VICD), commonly known tyoday as Procurement Control Dataset (PCD).

Figure 3

 A6: Visibility

Avoid at all cost having to install a part blind. The part location should always be visible during assembly operation. Having full visibility of the working area will ease assembly, and increase safety.

A7: Design parts with symmetry to ease assembly:

Design each part to be symmetrical so that the part does not have to be oriented for assembly. In manual assembly, symmetrical parts cannot be installed backwards, a major potential quality problem associated with manual assembly. If symmetry is not possible, make the part very asymmetrical. Refer to Figure 4.

Figure 4

Tooling

T1: Tool variety

Design for the minimum tool variety. Constantly having to change tool to install fasteners reduces efficiency and increase assembly cost.

T2: Common Tools

Design assemblies so the most common tools can be used. The best way to ensure the most common tools are used, is to go on the shop floor and ask.

T3: Assembly jigs

Design small assemblies to maximize self-alignment. Having to jigs increases cost.

Dimensions and Tolerances

DT1: Cost of Tolerance

Tolerance cost is exponential. Over tolerance increases rejects therefore increases cost. Refer to Figure 5.

DT2: Tolerance Step Function

The type of process depends on the tolerance specified. Each process has a practical limit regarding how close a tolerance can be held for a given skill level on the production line. Refer to Figure 5.

Figure 5

DT3: Tolerancing

Tolerancing is the most significant factor in the cost of a part, yet it is the most neglected factor. Both designers and machinists rely too much on the accuracy of CNC machine tools. Designers must avoid arbitrary decisions when specifying dimensions. Refer to Figure 6.

Figure 6

DT4: Tolerance Accumulation

To avoid accumulation of tolerance adjustment are necessary, make sure they are independent and easy made.

DT5: Manufacturing Process capabilities

Make sure that the tolerances specified on the parts are in line with the Manufacturing Process Capabilities. Specifying ±.005 when the best your Manufacturing Process capability is ±.010 will increase non-conformances.

Practical everyday DFM guidelines: They truly save time and money Part 2: Standard Parts

This Blog has spent a lot time talking about the philosophy of Design for Manufacturability (DFM). There are several good books on the subject of DFM and the reader can find in Amazon.com. Just type DFM in the search gadget.  We will nonetheless look at some of the very basic Guidelines to DFM, more specifically at Mechanical / Structural and System design guidelines that I picked up in Design For Manufacturability from David M. Anderson as well as other site on the internet. Part 2, we're looking at Standard Parts

Standard parts

SP1: Commercial Off The Shelf (COTS)

Never design a part that you can buy off the shelf.

SP2: Type of fasteners

Use common fasteners. Avoid exotic fasteners, and strive at using the same type of fastener throughout your design.

SP3: fasteners in stock

Always design with fasteners that are readily available from your stock room. Consult the inventory; avoid at all cost specifying fasteners that are not in stock.

SP4: Standardize parts

Standardizing parts will facilitate design activities; minimize the amount of part inventory. Handling and assembly operations will be improved. Common parts will result in lower inventories, thus reducing costs and increasing quality.

SP5: Minimize the number of parts in your design

Strive at design with a minimum number of parts, even standard parts. As the number of parts goes up, the total cost of fabricating and assembling the product goes up as well.

SP6: Design for common tools

Optimize the use of the same type and size of fastener so the same tools can be used throughout the assembly process.

 SP7: Small fasteners

Avoid using small fasteners that cannot be finger grabbed. If the operator has to use tweezers to grasp a fastener, assembly time will increase, therefore cost will increase. The same guideline applies to small components.

SP8: Certified Components

The aerospace industry requires certified components, which are typically more expensive that commercial ones. Imagine the cost of having to certify a component that you designed instead of looking for COTS.

SP9: Application

Use the fastener type that will meet the requirements of you application. However keep in mind all the guidelines in this section. If you feel there are some contradiction; you are right.

SP10: Simple part fallacy

Product designers see some parts as being simple to model, therefore simple to fabricate, therefore inexpensive. This is wrong. Refer to Guideline SP1.

SP11: Inexpensive part fallacy

Product designers see hardware (screws, bolts, nuts, rivets …) as being inexpensive, yet the cost of maintaining an inventory of multiple fasteners to suit everyone's taste can drive production cost up exponentially and drive efficiency down exponentially. Refer to Guidelines SP2 and SP3.

SP12: Fastener installation

Fastener should always be installed for a downward motion.

SP13: Tool Access

Some types of fastener require pneumatic tools that are bulkier than hand tools. Consider the tooling required to install the fasteners; refer to figure 1.

Figure 1

 SP14: Exotic Components

Avoid using Exotic Components. Exotic Components are typically more expensive, and their delivery problematic. If the supplier requires a minimum buy, the cost increases. Unless required on other projects, the unused components will stay in inventory, therefore increasing total cost further.

 SP15: Eliminate fasteners by combining parts 

The interface between two parts must be fastened together and also involves two sets of dimensions and tolerances. Combining part together eliminates the interface; the cost of manufacturing is reduced as an alignment is not required anymore.

Example: Aircraft components have gone from hundreds of sheet metal parts as shown in Figure 2, to one single machined part, thus saving thousands of man-hours in manufacturing.

Figure 2

Introduction to Integrated Product Development Team

Today, I am introducing the book "Introduction to Product Development Team".

This book is intended to young undergraduates and graduates entering the Air-craft Engineering world, or even any other type of industry. Aerospace Product Development evolves very fast and the computer tools and applications required to develop products evolve even faster. However, one needs to realize that to develop a product, tools and application are not doing the thinking and are not responsible for anything. There are roles and responsibilities shared between functions, evolving within a product development process where change is on the menu every day. Evolving in this environment can be intimidating. This books provides guidelines and introduces you to how a product is developed within a Product Development Process where the principles of Design for Manufacturability (DFM) and Concurrent Engineering are applied.

This book also introduces the concept of Product development integrated within a Product Lifecycle Management system where Work Breakdown Structures (WBS), Product Structures and Change Management are all inter-related.

Encourage me to continue developping this subject. The book is available in both Paperback format and in eBook Format. Available at LULU Publishing (eBook) or Amazon.com.

Practical everyday DFM guidelines: They truly save time and money Part 1: Geometries

This Blog has spent a lot time talking about the philosophy of Design for Manufacturability (DFM). There are several good books on the subject of DFM and the reader can find in Amazon.com. Just type DFM in the search gadget.  We will nonetheless look at some of the very basic Guidelines to DFM, more specifically at Mechanical / Structural and System design guidelines that I picked up in Design For Manufacturability from David M. Anderson as well as other site on the internet. The Guidelines are separated in 6 groups:

· Geometries (Gn)

· Standard Parts (SPn)

· Material (Mn)

· Assemblies (An)

· Tooling (Tn)

· Geometric Dimensioning and Tolerancing (GD&T)

Geometries

G1: Webbed Machined Parts

Make the inside corner radii of webbed, machined parts such as bulkheads, frames, beams, spars, formers and ribs, normal to the working plane. Avoid closed angle geometries that will require a ramp which add complication and cost to the part; refer to Figure 1.

Figure 1: Webbed Machined Part

G2: Driven Corner Radius

The side of an end mill creates the inside vertical corner radius. To assure tangential smoothness of the inside corner radius with the wall, the  corner radius should be designed with a radius slightly larger than the cutter radius. This is called; driven radius. By designing the corner radius oversize (consult the machinist), thus preventing the end mill smashing into the corner radius, causing undercuts, whiplashes or rope twist finishes. It enables the cutter to drive around the radius, instead of forming it with a size for size and mill cutter radius; refer to Figure 2.

Figure 2: Driven Corner Radius

G3: Fillets versus Chamfer

A Chamfer is typically less expensive than a Fillet. Unless necessary, stick to chamfering which can be done by hand, instead of programming the tool path of a special end mill. Refer to Figure 3. However, on primary structures, the fillet is preferred because of the fatigue cracks that can appear on the shaper change of geometry of a chamfer. Always consult the Stress Function.. 

Figure 3: Chamfer types

G4: Fillets and Corner Radius

Avoid excessive tool changes. Use one minimum radius size for all inside corners of a pocket. Use the same radius size for all corner, and same radius size for all fillets.

G5: Drilled Holes Size

Specify standard drill bit sizes. Unusual hole sizes bring up the cost of manufacturing through purchasing, inventory costs and generate tool proliferation. Always consult the machine shop.

G6: Through Holes

Through holes are preferred over blind holes. This has to do with the fact that a blind hole does not provide good chip exit and cooling.

G7: Reaming

Reaming after drilling is more easily conducted on a through hole.  However, Reaming add cost to the part. Reaming operations are usually required for pin installation or to prevent fatigue cracking in holes.

G8: Drilled surfaces

The entrance and exit surfaces of a drilled hole should be normal to the hole axis. Refer to Figure 4. Holes in the angled surfaces will require a spot-face normal to drill axis to prevent slippage.

 Figure 4: Angled drill Surface

G9: Number of holes and direction

Minimize the number of drilled hole sizes so that tool changes are minimized. Minimize also the number of directions on the part that holes must be drilled from so that setup time is minimized.

 

Figure 5: Surrounding geometry



G11: Tapped holes

Tapped holes cost more to produce than normal drilled holes.

G12: Access to Tools

Always consider the size of the tool required to assemble a component. For wrenches, consider the swing. Refer to figure 6.

Figure 6: Tool Clearances

 

G10: Surrounding geometry to hole

If there is protruding geometry surrounding a drilled hole, there may be risks of touching the geometry either by the drill bit or the drill chuck. Refer to Figure 5.

G11: Tapped holes

Tapped holes cost more to produce than normal drilled holes.

G12: Access to Tools

Always consider the size of the tool required to assemble a component. For wrenches, consider the swing. Refer to figure 6.

 G13: Hole depth

Deep, narrow holes with length to diameter ratios larger than three should be avoided. A drill bit will start to drift sideways at a depth .75 X Drill diameter, i.e.: a .25 Dia. drill with start wandering at .187” deep. The deeper the hole, the more chances you risk of breakage. One way to avoid a deep, narrow hole is to use a stepped entrance.

G14: Boring versus Drilling

Boring is more expensive than drilling, so drilling should be used if possible.

G15: Milling

Minimize the number of set ups required. Milling should be grouped into sets of parallel planes.

G16: Milling depth

Design milled pockets so that the end mill required is limited to 3:1 in length to diameter ratio. Longer end mills are prone to chatter. If long end mills cannot be avoided, clearances needs to be designed into the part. Refer to figure 7.

Figure 7: Milling Pockets

G17: Three-edge corner

When designing a three-edge inside corner, one of the inside edges must have a driven radius (refer to Guideline G2). Relief hole must be incorporated in the design. The hole must be drilled first since drills cannot withstand significant side loading. Refer to Figure 8.

Figure 8: Three Edges Corner

G18: Surface Flatness

For machined surfaces with a high degree of flatness, bosses should be used. The bosses are easier to control, clearly define the areas needing to be flatness controlled, and ensures stable assembly. Large flat surfaces for assembly are more difficult to control and unless highly accurate, therefore very expensive, will be a hyper-static assembly.

Software's: How do they affect Design for Manufacturability? Part 2: Integrating a CAD System?

CAD Systems have extended our capabilities in developing products. The time we took to create layouts, detail and assembly drawings in the days of the drafting table (and yes I am from that era) is greatly reduced. More and more we see integration of functions with tools and processes. However, is the work truly reduced for engineering or for the downstream functions dealing with the engineering data? Have we simplified our lives?

Duplication of tasks between Engineering and production functions is one of the leading causes of inefficiency and errors in the creation of Manufacturing Bills of Material (MBOM).  It is not uncommon for companies to maintain several version of a single BOM for any given job.  In most cases, a lot of time is spent creating a BOM within the CAD environment only to be re-typed into the ERP System, leading to increased man-hours and possible errors.  There are a few true off the shelf solutions  that integrate CAD systems and ERP Systems that enable extracting BOMs from the engineering definition , and import the data directly into the ERP system, eliminating typos and decreasing man-hours.  

Designer interaction with ERP Systems

My experience and I must admit to most product designers and engineers, an ERP system is an abstract system and as something that requires additional time and effort, for little to no value. One reason for this perception is that most ERP systems are not integrated with the design engineer’s design system. Such integration typically requires a lot of customization that will again typically be done in the middle of a product development project. Such situation only adds to aggravation and frustration and obviously makes ERP Systems even less appealing to product designers and engineers.

I was told once by a former President of Roll Royce Canada, that perception is everything when it comes to the customer’s view of a product or how a service is rendered. The product designers and engineers are the customers who are being served a system that is usually poorly explained, therefore not understood, which results in an outright rejection.  

Integrating Engineering with other Functions via ERP System

Unlike what most engineers believe, the world of product development doesn’t evolve solely around the engineering function. However, most product development datasets are issued from engineering using a tool solely used by engineering or designing functions; that is a CAD system. The closest to a CAD System any production function will get to is the viewing capability of the CAD System, as in many cases a 3rd party CAD viewer without writing rights, is used to consult the data from engineering.

It is important to understand that production functions should never work directly from the Engineering product Structure where all the product definition is defined. This is to avoid having the released engineering data tempered with by accident.  This is why it is best to avoid “2 way direct” ERP integration with the CAD System. Data should never be written from a CAD System directly into the ERP system’s database tables and that applies also from the ERP to the CAD System. The industry has realized this and, for the most part, moved away from this integration solution design. The reasons for this are:

• Writing data directly into the product structure or the ERP system can corrupt the product structure.
• Designers/Engineers should never write directly in the ERP system to avoid corrupting the Master Bill of Material (BOM).  Avoid having too many individuals entering data.  The corruption increases the total cost as cleanup is required to cleanse the Master BOM.

Example: MS20426AD5-5 is not the same as MS 20426-AD5-5, or MS20426-AD5-5

• Restrictions on updating software; if systems are tied too closely together, an upgrade of the CAD or ERP software or both in order to maintain integration between the two may be required.

Consideration when Integrating a CAD System to the ERP System

Although some CAD Systems can directly communicate with ERP systems, this integration is quite complex; from both a technical point of view as well as  a “workflow”. Some of the main issues to resolve in ERP integration with a CAD System include:

• Which system (CAD or ERP) is the authority?  Is it the product structure in the CAD/PDMS or is it the product structure in the ERP System?
• Who owns the data?
• Will the EBOM output from the CAD System need to be modified or will the CAD model contain the final complete BOM including all fasteners, packaging materials, lubricants, instruction manuals, etc.?
• How will employees in manufacturing have access to BOM info? (Viewer, CAD Models, Drawing or ERP system).
• Is the data input into the CAD System and passed to ERP, vice versa or both?  What is the interface?
• What are the attributes and who does the input into which systems?
• How will the initial input of items and BOM be handled and synchronized between the systems?
• How will revisions to items and BOM’s be handled and synchronized between the systems?
• How will you manage changes and non-conformance?
• How often will data be updated and synchronized between the systems?
• What is the trigger event for data input/output between the systems?
• What will be the driving attributes of the parts that will define a part?
• What about legacy data?

Downstream Impact when Engineering is not properly integrated

Lack of or no integration with downstream manufacturing planning activities will have the effects listed hereunder:

• Inability to reconcile EBOM to MBOM
• Inability to repurpose data to downstream functions, i.e.: Tech Pubs, Customer support, Supply Chain etc…
• Duplication of clerical tasks. Most of the information associated to a part definition in a drawing can be converted in attributes that will feed the ERP System. Attributes are like the DNA of a dataset that defines a Part,
• Errors due to duplication of tasks,
• More than one source of data, thus, introducing errors and duplicating data maintenance.
• Reporting of total cost of the product is seriously impeded,
• Difficulty to access the engineering data,
• Change management will be inefficient and ECO’s may increase, thus increasing cost,
• Inability to transition from a Drawing Based management to a Part Based Product management environment.

Closing Comments

Integrating a CAD System to the ERP system cannot be done in the middle of a product development project. To successfully implement this integration, team work between functional groups is paramount.  Engineering cannot do this alone and must work with the other functions that are generally speaking already integrated within the ERP System. It is quite a cultural change for engineering as for engineers are creator, not very good in data management. Yet, understanding data management when integrating a CAD System with and ERP System is just what is required from the engineers. Engineers need to see the added value of performing such integration, as depending of the way data is entered into the ERP System via the CAD System to ERP System Interface, the downstream function will be able to efficiently use the data or curse those who created the data. It’s garbage in garbage out.  

Software's: How do they affect Design for Manufacturability? Which CAD to buy?

Computer Aided Design (CAD) Systems have allowed us to become more creative in the way we work, but their ever evolving capabilities, power and time required to learn using them ultimately affects Design for Manufacturability. One must always remember that CAD Systems are just tools, nothing more.  

Here’s a good case study and a true story, to support this blog A company specialized in cabinetry design and manufacturing decided to put in place a top notch Engineering department, and to support it, they purchased a high-end Computer Aided Design (CAD) System with a high-end Product Lifecycle Management (PLM) System. The problem was not the applications themselves, but rather this company purchased the system without having a thorough understanding of the requirements associated to a Product Development Process (PDP). To make matters worse, there was no PDP in place at the time of the purchase.  This resulted in months (up to two years) of customization of the applications, while trying to fill customer orders, which in the end were very late, required numerous reworks, generated a significant financial loss and a no confidence vote in the systems put in place.  

Misunderstanding CAD Systems

It is not uncommon to see companies buying the wrong CAD System. This usually happens because we get blinded by the technology and some non-technical people truly think that it is the CAD System that designs the product. Ever heard the expression “Computer Designed” as a sale pitch? The CAD System is just a tool, and like any other tool, you need to know what you want to do with it before buying it. 

Consideration in the selection

Companies should develop their own considerations based on their PDP and products that ultimately leads to the selection of a CAD System. One cannot arbitrarily select a CAD System without answering (at least) the very basic questions listed hereafter and incorporate the answers in the requirements that will ultimately narrow the selection to one system. The perfect CAD System is the one that meets your requirements based on your PDP. Before putting a penny in a CAD System here are some points you should consider: 

• Purpose: What do you want to accomplish?
• Application: Aircraft, Marine, Space, Bridge, Building, Furniture, Electronics etc… Don’t try to shoot a bird with a canon,
• Ease of use—Productivity: Think of the people that will be using it,
• Training: How long is the training and how long to become proficient?
• Functionality: Consider what you need first, and then look into the nice to have. Consider the evolution of your business as well,
• Software Evolution: Some applications versions are not compatible with one another,
• Vendor stability: Make sure the selected vendor has a sound financial base, and a good track record,
• Support: Is it included, and how will future version affect your operation? Will you always need external support? Think $$$!
• Cost: it should be the last thing in your mind. Think of the Return on Investment (ROI) instead. Besides, accountants will always find the price too high, even if it’s a free open source CAD. Choosing the right CAD System that will increase productivity and reduce the design lifecycle is the only cost consideration that matters,
• Expert opinion: Ask for support from an independent CAD Expert not associated to any CAD supplier,
• Compatibility: think of compatibility with your production floor, especially if they work directly from 3D models,
• Suppliers and Customers: Do you need to be compatible with your suppliers or customers. E.g.: Aircraft OEM generally require full compatibility with their system,
• Manufacturing Functionalities: Does your CAD need to be integrated with the shop floor?
• Libraries: Is the CAD system compatible with commercial of the shelf standard parts libraries (bolts, nuts, screws…),
• Collaboration: Do you need collaboration functionality? It is useful when multiple designers work on the same assembly. This will tell you if you need a PLM application.

Your CAD Community

One of the building blocks of DFM is collaboration between functions. This is why you should involve all functions directly involved in the development of your product (except finance) to be part of the selection team. These functions should also have some level of proficiency in the use of the selected CAD System. Since they will be using a common tool, this will allow for a better collaboration among functions. 

The Ripple Effect

There is no stronger support for a CAD System then trust that it’s the right one, and trust in the PDP. This will lead to an efficient working environment where people will question how they can improve the system, rather than questioning the validity of the CAD system itself. Having the wrong CAD system in place will generate frustrations amongst functions and having no PDP in place to support the CAD will lead to people or functions working individually around the problem, therefore leading to a multitude of problems that will undoubtedly lead to a corporate wide disaster.

Closing Comment

Purchasing a CAD system requires knowing how one needs to work via a robust PDP and then list all the considerations supporting the PDP to purchase the right CAD System. There are professional consultants who are not associated to any CAD suppliers offering services that should be considered. Remember that once a CAD System is bought and put in place, only to find out you got the wrong one, will create a deep gouge on your bottom line.

Part Proliferation, Why it takes away your competitive edge? Part 4: Raw Materials

Last blog we looked at fasteners and how their proliferation affects your bottom line. In this blog we will look at Raw Materials. They have a direct impact on design, supply, and manufacturing total cost when standardized. If not standardized, it can drive up the total cost of your product.

An Aerospace company kept buying aluminum extrusions that had a minimum buy condition attached to them, and never seemed to deplete the stocks because every Engineer/Designer unknowingly specified different extrusions. However very close in dimensions, the extrusions were still different, therefore were ordered under different part numbers.   

If unchecked, raw materials can easily clutter a material storeroom. This clutter is created by the Engineers’ and Designers’ lack of visibility on what is in stock. Typically the choice of material will stop at what meets the immediate design need without regards to what is in stock, which in most case could do the job just as well.

Influence of Raw Materials,

Raw materials come in all shapes or forms that will later be transformed into components then be part of a product. Regardless of the industry, Raw Material can easily account for about 30% of the total cost of a component. Obviously, having our Aerospace Company as a scenario; inventory cost will be added over the already existing 30%.

Raw Materials are mainly classified by Format and Chemical Composition (or alloy in the case of metals, or essence for wood). Every variation of Format and Composition will generate a different material, therefore a different material stock number. Using our Aerospace Company as example; although the extrusions were aluminum alloy and shapes were the same, the extrusions shapes were of different dimensions, most of the time small differences. If the Engineers/Designers would have been aware of what was in stock, they could have designed their components around one single extrusion, thus avoiding the thousands of dollars in inventory. 

Considerations in selecting Materials

From what was discussed above, it is very obvious that one should select a raw material that is stock in the factory. However if what’s in stock doesn’t work, before selecting a material, consider the following:

• Number of parts that will be fabricated: Part volume can drive the selection of material format, as well as the transformation process.
• Availability of the material: Exotic materials are expensive and create delivery problems and are likely to have a minimum buy clause attached. Common raw materials are generally available and delivered within 24 hrs.
• Make from: Can existing parts be used as raw material and modified to suit the need? This will save time in design and minimize inventory.
• Corrosion: What are the environmental conditions? Are you dealing with dissimilar materials that can generate galvanic corrosion?
• Stress:  Vibration, creep, fatigue, strength, cracking, etc...
• Toxicity: Some materials generate toxic fumes when processed, e.g. beryllium copper.
• Dimensional Stability: Dimensions can be affected by temperature change, humidity levels, etc.: e.g. wood expands under humidity, Stainless steel warps when welded, etc...
• Transformation Process: Machinability, weldability, Formability, e.g.: Some aluminum alloy cannot be welded; Stainless Steel has poor Machinability, etc...
• Surface Protective Finish: Can it be avoided? Some metals do not require protection. Stainless steel can replace a painted carbon steel part, and will save the costs associated with painting parts.
• Environmental: Chemical transformation processes are harmful to the environment. Think green when you select a material or when specifying a Chemical process.

Raw Material initiatives

Raw material selection is done at the Design Process level, therefore should be defined as early as possible, and should be kept as much as possible to what is stock or easily available. Designers are solely responsible for material selection, and indirectly define the manufacturing process by design. This is the main reason why manufacturing and Material Management need to be involved early in the design process in order to design manufacturing and material management into the product. This exercise will also help defining a preferred raw material list.

The Ripple Effect

Having a preferred material list will have ripple effect on engineering activities, as well as purchasing and manufacturing. Having engineering use company standard raw materials minimize design uncertainty of using a new material which very often require testing and certification. It will minimize material shortage and having to buy materials with a clause of minimum buy. It will also maximize savings since the same material can be purchased at a higher volume. Manufacturing will be more stable since the mechanical behavior of the company standard material used are known and controlled. At the end of the day, it will help minimize the design and manufacturing life cycle.

Closing Comment

Raw materials are often taken for granted and the selection is done by Engineering with little regards to the production process that follow. This is not done maliciously, but  it is the result of a lack of visibility very often not given to Engineering as the everlasting motto is still being used; Engineering defines the WHAT, and Production defines the HOW.  Engineering and production function should define the materials concurrently so availability and manufacturing process stability is designed into the product.