Month: August 2009 (page 1 of 2)

Milled buckle

Here is a milled aluminum buckle still attached to the blank it was machined from. If you look closely, you can see both striations and faceting on the surfaces from the cutter. The striations come from the “stepover”; the amount the ball nosed cutter is moved over for each successive traverse across the part. The faceting comes from approximating the curve of each traverse by moving the cutter in thousands of tiny straight line moves. Both of these parameters can be set during programming. A smoother less faceted surface comes at the expense of longer cutting time so a compromise is chosen depending on the needs of the customer. This part was cut with a 0.0938″ diameter ballcutter with a stepover of 0.005″ and approximates the curve within 0.001″. The cuts required 1/2 hour run time per side including picking out the corners with a smaller cutter.

Quality and Cost

Quality and tooling cost are a subject I’m asked to comment on frequently, particularly with the decline of North American manufacturing and the rise of overseas manufacturing to take its place. As with all things, there are tradeoffs to be made, particularly since it’s quite difficult to be assured of quality tooling when it’s commissioned from far away.

That still means your best hope for success is to commission North American tooling, unless you can find a vendor to partner with, who has lots of experience overseeing its tooling procurement from abroad and can help you pick sensible circumstances under which you can benefit from the cost advantage. Only a seasoned molding company can do this reliably: we’ve partnered with a very well-regarded, quality conscious Vancouver company, and have them commission tooling abroad whenever it’s the best way to meet our customers needs. However, all of our logistically complex projects are tooled in-house to mitigate the problems of long supply chains, intellectual property protection and uncertain communication.

Quality is not cheap, and there are plenty of competitors who offer extremely inexpensive tooling and like to pretend that it’s just as good as a quality tool and can give you what you need. That’s not quite true if your needs are more sophisticated than the roughest of plastic parts and if you can’t accept production delays from tool breakdown.

I’ve shown a few shots of some typical problems that have crossed my desk over the years and are worth thinking about when you’re setting tooling goals and budgets, as well as when you’re choosing a tooling and molding vendor.

Here is an example of two mold components, one made to a low standard out of soft steel; one of hardened toolsteel and built to a high standard. Each has run many tens of thousands of parts, and the difference in condition is remarkable. The upper slide is good for many more parts, whereas the lower slide is about ready to be junked along with the rest of the tool. Each served its purpose adequately, but many unscheduled repairs with resulting production losses occurred with the low quality tool.

Sometimes the construction quality just can’t compensate for sloppy handling: here is a mold core I built, that was ruined in a very short time by allowing drool from the injection nozzle onto the parting line until the core was so squashed that the part would no longer release from the mold. Less than 5000 shots destroyed this core.

Here is a shot of the hotside ejector box and the sprue bushing on the same mold after less than 6 months of service. Needless to say, the customer was furious, at the extensive damage to this $30,000.00 tool. The message is pretty obvious: a quality molder will protect your investment, and save you money in the end. Our molding partner produces first-class quality work and will look after your investment properly.

Here’s an example of a poorly made mold component that’s been abused as well. This is typical of low cost molders, whose relentless focus on their short term bottom line motivates workmanship of this quality. Of course, it must be said that they do create successful, “good enough” parts from this tool, so if your requirements can be met with this business approach, it’s a perfectly valid one. Just don’t come to me for this kind of tooling!!

Here’s a detail shot of the core, showing how rough the construction is and how badly it was damaged in use. The arrow points to a shutoff that was squashed to the point that the tool became non-functional. The tool shows evidence of never having been properly fitted together when it was made; it was simply rough machined and then mashed together in the molding press.

A typical mold

Shown is a mold I’m just finishing up (as of August 2009). It makes a family of small dental parts using interchangeable cores and slides. I’m going to run one experimental cavity first, measure the finished plastic parts, and then cut the remaining cavities as needed to get the very tight tolerances demanded in this application.

This is a good example of a medium to high volume production mold and has fully hardened tool steel parts wherever high wear or strain will be encountered. Everything is fitted very precisely and the finished mold is expected to produce parts at the rate of 4 parts every ten seconds. A mold like this costs around $20,000.00 to build.

On the right is the hotside…it’s where the molten plastic is squirted in under huge pressures, about 4000 PSI for these parts. You can see the outer mold cavities, the runners and the beryllium copper cores for the center parts and the locks that move the slides and hold them against the injection pressure. On the left is the coldside. Visible are the two slides with their cavities. The slides move together when the hotside is squeezed onto the coldside by the molding press; 17 tons of clamping pressure will hold the mold halves together. You can also see the ejector pins pushed forward.

These are all the mold parts. Typical tolerances are +/- 0.0002″, so everything needs to be precision ground. Molds are highly stressed during use: the pressures are so extreme that a mold failure can cost a life, so everything is very heavily built from prehardened steel or hardened toolsteel. Also shown are some of the electrodes needed to burn the cavities and the fasteners, springs and other odd bits needed to make this tool. Two of the slides are missing; they were still in the EDM machine when the shot was taken.

Shown is one of the slides with a center mold cavity; my thumb on the right side of the shot provides scale. You can see a cavity half, and the shutoff face on which the beryllium copper core locates, also the runner and the gate which feeds plastic into the cavity.

All that to make this tiny part!! This is the same photo that is shown in the miniature machining section, and is, of course, a picture of the machined prototype part, not a molded part. I’ll update this shot when I get parts out of the mold.

The molded parts ready for testing. There are 6 different configurations of this part. All the mold cores will now need to be tuned to make these parts fit perfectly to their mates.

Graphic Design

Three versions of a personal escape device for three different applications are shown.  All of these JPG files were rendered using Photoworks  and became the background graphics for brochures.  It was an interesting challenge to render the transparent yellow  plastic hood and the ribbon at its edge.

The customer requested a more severe, “architectural” look for one of the center pages; this file was created in response to that request.

The texture of the pleated filter paper in this version required a bit of manipulation to get decent contrast: it is a bitmap overlaid on the Solidworks model.

Aircraft Assembly Fixture

These clamping devices need to have a textured gripping surface of a specific roughness. Sinker EDM is a good means to achieve that goal. Shown are a before and after picture. The parts are hardened tool steel and the heads are about 1 inch in diameter.

Production Laser Welding

Surgical Screwdriver Gears: These are welded in batches of 200 parts per order using a custom fixture to align the parts and present them accurately to the laser beam. They are 17-4 PH stainless steel.

Production Milling

Surgical Screwdriver Handles: These are milled from 6061 T6 aluminum alloy and glass beaded then clear anodised. Lot sizes are typically 200 parts per order.

Production Plastics Milling

Telephone Handsets: These are typical milled plastic parts usually run in lots of several hundred at a time. We mill all manner of plastic enclosures, usually to create openings for cable connectors, switches, displays etc. We have developed a proprietary process to fixture these parts that prevents marring them during machining.

Production Grinding

Surgical Screwdriver Clamps: The material is 303 stainless steel and the lot size is 400 parts. They are form ground 10 at a time in a fixture. (Now replaced with metal injection molded parts)

Production Turning

Brass Collets:These were run in lots of 15 units per the customer’s request. The parts are about 3/4inch long and the material is leaded brass.

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