Al LaVezzi
President
LaVezzi Precision Inc.
Glendale Heights, Ill.
Today’s successful designers must not only use their engineering backgrounds to formulate ideas, they must also be good communicators. Transferring ideas to the CAD screen or the drafting table is just the first step. Communicating those ideas to people who can bring the project to fruition is the second. And communicating with your machining vendor is an integral part of that second step.
Designers simply cannot maintain the experience level that manufacturing engineers must have to stay on the cutting edge of machining technology in this constantly developing environment. That’s why many engineers turn to machining vendors for help and advice. Here are some guidelines for getting the most out of your relationship with a precision machining vendor.
Opening communications with a vendor
After the first stage of a product development project — conceptualization — the device designer and precision machining vendor should begin talking to each other. Topics should include preliminary specifications, expectations of both the OEM and the vendor, aspects of the device’s initial development, prototyping and production, as well as the economic feasibility of the project.
Good initial talks typically spawn visits to prospective vendors’ facilities. This offers engineers the chance to check out the company and its management. They will also be able to get a firsthand look at the sophistication of the operation and personnel. Also, the capabilities listed in the facility’s equipment list can be evaluated. On-site visits offer design engineers the most effective and efficient way to begin new partnerships. It also helps build trust between the designer and vendor on a personal level.
If practice dictates, a confidentiality agreement may be required prior to any discussion. This can make communication more open and comfortable. It also lets the OEM draw on the manufacturer’s knowledge early in the design stage to come up with a more buildable and cost-effective design.
Keeping up with manufacturing
The next step is to learn the capabilities of today’s precision machine tools. Thirty years ago, CNC radically changed the metalworking industry. Since then, global competition in the machine-tool industry has constantly been expanding the parameters within which manufacturing engineers work. Now we have multiaxis controls directing multiaxis tools that can generate an unlimited number of facets on a part, and turning centers with the latest in cutting materials — coated carbides, PCBN, PCD and ceramic — that deliver tolerances previously held only by grinding. Enhancements, such as controlling spindle rotation and live tooling off-center motion can handle machining tasks previously performed on multiaxis mills.
Machining centers with high servo gain can accurately sculpt shapes and forms in five axis of motion. CNC grinding centers utilizing workhead control generate out-of-round shapes with fine surface finishes. Extremely precise Swiss turning equipment utilize 8 to 10 axes to produce complex devices in one operation. Improvements in the accuracy of ball screws and resolvers of this equipment mean that precise tolerances can be held every time.
The latest CAD innovations let manufacturers view parts being machined on screen prior to making an actual cut, which facilitates the production of error-free first pieces. This software also lets manufacturers more accurately estimate the cost of a part.
Try to match the vendor’s equipment and facilities list with your part requirements. For example, does your part require wire-EDM or contour grinding? For every operation that a vendor cannot do in-house, there is an increased risk of quality or delivery issues.
The manufacturing engineer should always be willing to share his knowledge and expertise with designers to instill confidence in his ability to deliver the required product. Look for helpful advice regarding tolerance, fits, and finishes. Prior to solidifying a design, ask the engineer to evaluate the design from the manufacturing feasibility viewpoint and to make any necessary recommendations.
Can the vendor certify the work?
The third step is making sure you work with vendors who have the facilities and accreditation to fully inspect and certify their work. Device manufacturers and OEMs are not in the inspection business and many times do not have the facilities or personnel to verify that components meet the specifications. Therefore, it may be more practical to have an outside source inspect and verify the product. Two avenues are available: contract inspection services or the component manufacturer. Contract inspection services can do final or first piece inspection verification. The drawback is the additional lead-time and expense.
But the right choice usually is to make sure your selected manufacturer has in-house capabilities to inspect and verify that components are manufactured per specifications. This includes having the proper inspection, measuring and test equipment, as well as properly trained personnel. Ask for a formal inspection report on the final product, using either your own format or the vendor’s. Inquire if your selected vendor has any ‘ship-to-stock’ arrangements with their customers.
The ultimate goal in partnering with a contract manufacturer is to have incoming parts bypass your inspection department and go directly into stock, thus saving the time and expense of re-inspecting the parts. Your vendor-of-choice should also be accredited to fully certify their work. An experienced medical device manufacturer, for example, should have FDA Certification and thus be following the Good Manufacturing Practices set forth therein.
Inspection and certification aside, the burden of quality (i.e., adherence to specification) remains with the vendor. Your design must include the minimal requirements for proper fit, form, and function, and you should expect these specifications to be met 100% of the time. Never accept the excuse, “That’s as good as we can do,” from a vendor who has oversold his capabilities.
Provide all the specs
It is essential that designers supply accurate and complete specifications as part of the formal contract with a manufacturing vendor. Specifications, whether listed on a formal drawing or on the purchase order, help ensure that all intents of the designer are fully understood by the vendor and that they can be met. Certifications covering raw materials or any required heat treatments, plating or passivation treatments, should also be included in the contract.
At a minimum, specifications should include:
• Material specifications (with ASTM specification for implants).
• Surface finish requirements.
• Default dimensional tolerances (i.e., XXXX = ±.0005 in.).
• Maximum and minimum corner breaks or chamfers.
• Maximum and minimum filet radii.
• Plating and passivation specifications.
Make sure the tolerance requirements are tightened to suit design requirements and that nonfunctional surfaces are dimensioned accordingly. Default values in CAD systems must be adjusted so that three or four decimal values are not used inadvertently. Also, when transmitting CAD drawings electronically to a vendor, convert them to an industry standard file format before sending them.
If you decide not to go with a “hard drawing” during the prototype stage, the vendor must be willing and able to work with electronically transmitted drawings. Usually it takes a higher degree of trust and confidence before this occurs, as verbal communication may replace some aspects not yet formally stated.