Part Design with Manufacturing in Mind

Posted by Al Timm on May 28, 2013 3:00:00 PM
Al Timm

blank.pngAlmost any reasonable design looks good on paper (or even as a prototype)—but that doesn’t mean it’s a sure thing when it comes to manufacturing it. In some ways, designing the product is easy compared to making sure it can be manufactured in a streamlined, efficient, validated, and repeatable way.

Manufacturability impacts profits. By improving the part design, material selection, and/or the process design (enhancing manufacturability) to make sure a high-quality product is manufactured in a fast and accurate way to meet or exceed customer objectives, a huge amount of money can be saved over the lifecycle of the product.

Quite simply, “part design with manufacturing in mind” will determine the success or failure of a project.

The first step is getting the customer design team and the injection-molding engineering team together to discuss every aspect of the project, including intended end use and lifecycle expectations. Feasibility reviews early in development can avoid costly tooling. Production manufacturing should always be the end target when designing parts and tooling. Decisions made during these design meetings typically account for about three-quarters of the total final cost of the part or product—so a lot of money is on the line.

Part design and tool design are dependent on each other and thus should be done concurrently—hopefully in the earliest design stages. The cross-functional engineering team (tooling, materials, manufacturing, and quality engineers) must be involved early to provide a realistic manufacturing perspective on product design, tolerances, mold component functionality, mold materials, tool design, material performance, operational constraints, and associated costs.

The team especially looks for any potential problems in part geometry or tolerance that might result in poor steel conditions or require special tooling features such as lifters, slides, and threading/unthreading. The physical and chemical properties of the selected resin are also evaluated so that the proper mold steel can be selected and mold cooling be reviewed. Mold flow evaluation is also undertaken to determine the best type of gate and gate locations, in addition to determining proper vent locations.

Taking these steps up front is the best way to eliminate wasted effort and rework, which adds significant cost to the tooling budget.

Manufacturability review includes confirmation of standard plastic design practices and incorporation of tooling details to create the most robust design possible. Tooling specifications and tooling sources are finalized and purchased component sources qualified. A comprehensive process failure mode effects analysis (PFMEA) is also completed. Below are some key goals when designing a product with manufacturability in mind:

  • Eliminate or replace, where possible, unusual parts or specifications that add complexity

  • Review material supplier recommendations for selected resins

  • Design parts with nominal wall thickness whenever possible

  • Where possible, eliminate or combine steps to increase manufacturability

  • Gate into the thickest wall section of the part, with a gate designed for minimal to no trimming

  • Design parts with adequate draft for proper release from the mold without the use of mold release agent

  • Design parts to minimize secondary operations, such as assembly or finishing

  • Design parts with generous radii at part geometry intersections to enhance melt flow and reduce stress

  • Consider aspects of the tool design when designing the part (such as keeping knit lines and end-of-fill locations in mind when choosing gate locations)

  • Once a reasonable design has been made, complete a mold flow analysis, including melt flow, warp cooling pressures, knits, etc. 

For good reason, customers are concerned about cost. The best way to reduce cost, and maximize overall profitability, is by working closely with the injection molder to consider all the design details that will, in the end, result in the highest manufacturability of the product. It will be time well spent.

Designing for Critical-Use Automotive Applications Guide