The fast track to injection-molding tooling

Dec. 2, 1999
The ability to acquire tooling fast is often the key factor that determines commercial success.

Marc Dubreuil
General Manager
PTA Corp.
Oxford, Conn.

Edited by Jean M. Hoffman

The importance of time-to-market in product development is no secret. Having a product hit the shelves even just two months sooner than the competition can give a new product a headstart that the competition cannot overcome.

There is no shortage of management philosophies, buzzwords, software, and hardware technologies that promise to compress timeto- market cycles. Some of these — including early vendor involvement (EVI) and concurrent engineering (CE) — are great strategies on paper and sometimes work well. In other instances, they are just management’s euphemism for getting engineers to do seven things at once.

For example, when new designs incorporate injection-molded parts, tooling is commonly one of the longest lead-time articles. Efforts to compress the development cycle by reducing the time it takes to acquire tooling is both valid and risky. Done right, weeks or even months can be gained. Done wrong, equally as much time can be wasted.

Making tooling for injection molding is a specialty unto itself. It requires the simultaneous consideration of structures, cosmetics, costs, sourcing, delivery, and two separate production issues — the tool itself and the parts being molded.

Key to compressing tool-acquisition cycles is finding a tooling house that does more than just talk about EVI, CE, fancy solid-modeling capabilities, and so on. They must plan thoroughly and have good process methodologies that they follow rigorously, instead of just diving in and making chips as quickly as possible. Using the newest software and metalworking technologies helps cut time from a project. But there first needs to be defined management strategies to use these tools effectively. These strategies can be grouped into stages of planning, manufacturing, and sampling.

The three main tasks of planning are project management, tool design, and outsourcing components and services.

Project management — CE lets tooling vendors plan and resolve geometry problems early enough to redesign tooling before changes become too unwieldy or expensive. And although efficient tooling houses often turn around complex tools in six weeks or less, early resolution of these issues is critical for compressing the design cycle. More time can be saved by selecting resin and color at this stage as well, because resin delivery lead times often range from six to eight weeks.

Unfortunately, CE may not be feasible for product developers who face numerous design and engineering issues. The problem is that they often can’t spend the necessary time working with vendors on downstream manufacturing. Instead, they must gather the information or analysis during the bid process. Identifying a good vendor at this stage often requires gauging how each one responds to the proposed project.

Often a vendor will standout by asking the most questions or voicing concerns about potential problem areas in the design while they’re assembling their bid. Moreover, a wise tooling vendor will not proceed, even after the PO is signed, until a good data base is available. Skipping this step and proceeding immediately to cut metal often results in the unwary tool maker painting himself into a corner, with the only escape being time-consuming rework.

A tooling vendor should also be able to demonstrate a refined system of gathering, distributing, and integrating all the necessary information throughout the project. This should include a foolproof plan for tracking design changes and other decisions as they take place and distributing only the most current version of the data to concerned parties. Furthermore, a new design must be reviewed for manufacturability early in the development cycle, especially when parts are to be injection molded.

Few product designers are adept at designing parts optimized for injection molding. Therefore, it is to their advantage to review manufacturability from as many points of view as feasibeble. Some questions which are always helpful include: Is the part moldable without voids, sink marks, and knit lines? Can it easily emerge from the mold? Are radii and section thicknesses specified for optimum strength and will the part look good? Will it be susceptible to warp or internal stresses? The tooling vendor’s project manager must look at these and many other issues as early as possible.

Resin selection is also critical. It significantly affects mold filling and cosmetics as well as structural performance. Changing section thicknesses or radii may force a reanalysis of the design’s structure to ensure the specified resin still performs as required. Manufacturers who don’t fully understand the engineering parameters of resins and those who lack FEA capabilities may need the toolmaker to confirm their resin choices. Often toolmakers have such expertise and can identify possible mold-filling problems or recommend moldflow analysis that helps avoid unnecessary rework or project delays.

Tool design — Molding problems identified during planning are addressed in tool design. Section thicknesses, radii, and drafting of certain parts may need modification at this stage. And in some cases, it is advantageous to have the tooling house make such changes if the product developer lacks the time or resources. However, a system must be in place to accurately and efficiently track any changes.

Ironically, the most sophisticated part-design programs are often the least amenable to quick, simple changes. Simpler programs such as AutoCAD and Cadkey can make design changes easily and quickly. These programs have proven to be efficient editing tools, once macros and templates are in place for the many repetitive elements used during tool design. However, developers must understand that the “patches” implemented via AutoCAD or Cadkey are only to let the mold tool go into production sooner. Once the pressure is off, the permanent database will need updating to reflect these changes.

Outsourcing — Tooling vendors often outsource components and services that are critical to the finished mold tooling. These include components such as hot runner systems, lifters, unscrewing devices, and large, customdesigned mold frames. Farmed-out services may include specialty EDM, engraving, texturing, and polishing. Obviously, subcontractors need CAD files as early as possible for long leadtime items. Not all items are suitable for outsourcing. Placement of work outside or in-house hinges on factors such as quality, deadlines, and of course cost.

One of the most basic decisions concerns tooling material. There are several, sometimes conflicting, issues to consider. For example, aluminum tooling is less expensive and faster to machine than steel, but steel is more durable and better suited for long production runs. Steel also handles high-temperature processing better. For small molds, material selection has little impact on delivery and price. But the material used for large molds can change delivery time and price by up to 30%. In many cases, fast-turnaround tooling is a hybrid with an aluminum main body and steel inserts for areas with critical tolerances and those seeing high wear. Thus, tool material must be confirmed early in the design process as well.

The newest machine and EDM tools are so fast that they can shave off one or two weeks worth of machining time for large, complex tools. In addition, sophisticated control technologies now run machine tools unattended aroundthe- clock. Smart EDM controllers automatically adjust to machine conditions, frequently optimizing tool speed and controlling surface finishes well enough to eliminate polishing and finishing work.

Unfortunately, there can be a significant amount of time wasted during tool production spent searching for information that isn’t on the print or in the database. What complicates the matter is that decisions on gating, injection, ejection, and cooling may be dispersed among the project manager, tooling engineer, or client. Inadequate documentation forces the machinist to spend hours hunting down and confirming necessary information. But shop-floor computers networked together can help mitigate the problem. They can give machinists instant access to paperless project files and let them quickly find answers to virtually any question independently, regardless of time of day.

Ideally, the first part out of the mold will be perfect. The sampling or testing phase should then be minimal or nonexistent and the part can go directly into production. But often there are problems such as voids, knit lines, or other mold-flow issues. A mold-flow analysis during the design phase can help avoid such difficulties. It should be noted, though, that mold-flow analysis is still an inexact science and should be used to augment design principles and experience.

In most cases troubles that surface during sampling can be quickly corrected by modifying simple procedures. Sometimes a quick tweaking of melt temperatures, injection and holding pressures, or dwell time can solve the problem. Minor changes to the mold tool might also be necessary, so the faster such changes take place, the better. The need for fast changes underscores the benefit of sampling at the tooling vendor’s facility, provided it has the appropriate injection-molding equipment.

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