A customer's prescription for MIM precision

Bob Alvarez says his company has been working with MIM for some time now. Alvarez is a consulting engineer for Ethicon Endo-Surgery (EES), a division of Johnson & Johnson (Cincinnati, OH). EES is recognized worldwide as a leading surgical instruments manufacturer. As a customer, he has felt your pain, your new industry's growing pains, that is. What's hurt the worst? Alvarez says poor feedstock compounding control and a lack of sophistication in molding.

Compounding. Initially, he says, high MIM shrinkage rates hurt in holding dimensions. He explains that there were few good feedstocks, because poor compounding techniques were being used. This problem was augmented by a lack of understanding of modern compounding theories. Alvarez believes premier MIM molders like Thermat and PCC-AFT have resolved this issue.

Molding. Alvarez says he gets better results from molders using pressure-transducer control. With such control, molders can maximize yield by minimizing shot-to-shot variation in parts caused by powder/binder separation during injection. He says you cannot hope to hold tight tolerances without closing the loop.

MIM is a core technology to minimally invasive endoscopic instruments, an EES specialty. Small, complex, precision components like disposable jaws and graspers could not be produced cost effectively in high volumes without MIM. Alvarez points out the MIM jaws in his company's latest Allport product as a prime example. "The PIM industry is just now beginning to improve on these issues of compounding and injection molding," he concludes.

Precision MIM Preventive Medicine

Ethicon Endo-Surgery's Bob Alvarez has technical advice for those interested in getting into MIM:

  • Establish a consistent raw material. This will make or break the project.
  • Purchase injection molding machines equipped with powerful computer controls and pressure transducers both in the mold cavity and in the nozzle.
  • Review your screw designs. GP screw technology will not work.
  • Sintering equipment must minimize temperature gradient effects. Continuous sintering is best, but it's impractical for low-volume production.
  • Establish a good foundation for prototyping MIM parts.

    Contact information
    Ethicon Endo-Surgery Inc.,
    a Johnson & Johnson Co.
    Cincinnati, OH
    Bob Alvarez
    Phone: (513) 483-8122
    Fax: (513) 483-8928
    Web: www.ethiconendo.com
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