Tool Design - DFM - Points to REMEMBER...

A1) Understand manufacturing problems/issues of current/past products:-

In order to learn from the past and not repeat old mistakes, it is important to understand all problems and issues with current and past products with respect to manufacturability, introduction into production, quality, repairability, serviceability, regulatory test performance, and so forth. This is especially true if previous engineering is being "leveraged" into new designs.

A2) Design for easy fabrication, processing, and assembly:-

Designing for easy parts fabrication, material processing, and product assembly is a primary design consideration. Even if labor "cost" is reported to be a small percentage of the selling price, problems in fabrication, processing, and assembly can generate enormous costs, cause production delays, and demand the time of precious resources.

          P1) Adhere to specific process design guidelines:-

It is very important to use specific design guidelines for parts to be produced by specific processes such as welding, casting, forging, extruding, forming, stamping, turning, milling, grinding, powdered metallurgy (sintering), plastic molding, etc. Some reference books are available that give a summary of design guidelines for many specific processes. Many specialized books are available devoted to single processes.

           P2) Avoid right/left hand parts:-

Avoid designing mirror image (right or left hand) parts. Design the product so the same part can function in both right or left hand modes. If identical parts can not perform both functions, add features to both right and left hand parts to make them the same.
Another way of saying this is to use "paired" parts instead of right and left hand parts. Purchasing of paired parts (plus all the internal material supply functions) is for twice the quantity and half the number of types of parts. This can have a significant impact with many paired parts at high volume.

           P3) Design parts with symmetry:-


           Design each part to be symmetrical from every "view" (in a drafting sense) so that the part does
           not  have to be oriented for assembly. In manual assembly, symmetrical parts can not be installed
           backwards, a major potential quality problem associated with manual assembly. In automatic
           assembly, symmetrical parts do not require special sensors or mechanisms to orient them
           correctly.

           The extra cost of making the part symmetrical (the extra holes or whatever other feature is
            necessary) will probably be saved many times over by not having to develop complex orienting
            mechanisms and by avoiding quality problems.

P4) If part symmetry is not possible, make parts very asymmetrical:-

           The best part for assembly is one that is symmetrical in all views. The worst part is one that is  
           slightly asymmetrical which may be installed wrong because the worker or robot could not notice
           the asymmetry. Or worse, the part may be forced in the wrong orientation by a worker (that thinks
           the tolerance is wrong) or by a robot (that does not know any better).

           So, if symmetry can not be achieved, make the parts very asymmetrical. Then workers will less
           likely install the part backward because it will not fit backward. Automation machinery may be
            able  to orient the part with less expensive sensors and intelligence.

P5) Design for fixturing:-

           Understand the manufacturing process well enough to be able to design parts and dimension them
            for fixturing. Parts designed for automation or mechanization need registration features for
           fixturing. Machine tools, assembly stations, automatic transfers and automatic assembly equipment
           need to be able to grip or fixture the part in a known position for subsequent operations. This
           requires registration locations on which the part will be gripped or fixtured while part is being
           transferred, machined, processed or assembled.

P6) Minimize tooling complexity by concurrently designing tooling:-

           Use concurrent engineering of parts and tooling to minimize tooling complexity, cost, delivery
           leadtime and maximize throughput, quality and flexibility.

P8) Specify optimal tolerances for a Robust Design:-

           Design of Experiments can be used to determine the effect of variations in all tolerances on part or
           system quality. The result is that all tolerances can be optimized to provide a robust design to
           provide high quality at low cost.

P9) Specify quality parts from reliable sources:-

           The "rule of ten" specifies that it costs 10 times more to find and repair a defect at the next stage
          of assembly. Thus, it costs 10 times more cost to find a part defect at a sub-assembly; 10 times
          more to find a sub-assembly defect at final assembly; 10 times more in the distribution channel;
          and so forth. All parts must have reliable sources that can deliver consistent quality over time in the
           volumes required.

The Rule of 10

Level of completion     Cost to find & repair defect
    the part itself                     X
    at sub-assembly               10 X
    at final assembly             100 X
    at the dealer/distributor 1,000 X
    at the customer             10,000 X

P10) Minimize Setups:-

For machined parts, ensure accuracy by designing parts and fixturing so all key dimensions are all cut in the same setup (chucking). Removing the part to re-position for subsequent cutting lowers accuracy relative to cuts made in the original position. Single setup machining is less expensive too.

P11) Minimize Cutting Tools:-

For machined parts, minimize cost by designing parts to be machined with the minimum number of cutting tools. For CNC "hog out" material removal, specify radii that match the preferred cutting tools (avoid arbitrary decisions). Keep tool variety within the capability of the tool changer.

P12) Understand tolerance step functions and specify tolerances wisely:-

The type of process depends on the tolerance. Each process has its practical "limit" to how close a tolerance could be held for a given skill level on the production line. If the tolerance is tighter than the limit, the next most precise (and expensive) process must be used. Designers must understand these "step functions" and know the tolerance limit for each process.

The Importance of Good Product Development

C Good product development is a potent competitive advantage.

C Product design establishes the feature set, how well the features work, and, hence, the marketability of the product.

C The design determines 80% of the cost and has significant influence on quality, reliability and serviceability.

C The product development process determines how quickly a new product can be introduced into the market place.

C The product design determines how easily the product is manufactured and how easy it will be to introduce manufacturing improvements like just-in-time and flexible manufacturing.

C The immense cost saving potential of good product design is even becoming a viable alternative to automation and off-shore manufacturing.

C True concurrent engineering of versatile product families and flexible processes determines how well companies will handle product variety and benefit from Build-to-Order and Mass Customization.