Prepare for Better Vibration Tests
Wayne Tustin, Equipment Reliability Institute, Santa Barbara, CA, Rick Smith and Dan Reeder, Wyle Laboratories, El Segundo, CA- October 1, 1999
When you seek the services of an environmental test laboratory, you can expect the staff to ask many technical and procedural questions. The staff will ask about your reasons for performing the tests, whether you have a test specification, and what your deadline is. They also will ask questions about the product itself.
Labs need to ask these questions to provide the right level of service. The more details you can work out in advance, the smoother and quicker the tests will go—and the better chance you have of getting the results you desire. If you don’t make the effort to develop a full test plan with the lab, you might end up with abysmal results.
Consider the project engineer from an aerospace company who called Wyle Laboratories several years ago. This customer wanted to run a shock test on a small electronic package. His team was behind schedule on a year-long R&D effort. If they didn’t finish development within a month, they could lose funding.
The customer wanted to conduct an impact test from a 5-ft height. When asked for a written procedure, the customer claimed he didn’t have time to provide one. The more questions the lab’s engineers asked, the more upset the customer became. Finally, he decided he would serve as his own test director, asking the lab to provide a shock machine and a test crew.
On the day of the test, he selected a lightweight shock machine designed to test to the Navy MIL-S-901 standard. After technicians secured his specimen to the machine, he directed them to raise the machine’s hammer 5 ft. The warning buzzer sounded, and the hammer fell. Upon impact, the retaining bolts sheared, and the specimen bounced across the laboratory floor. The tangible result of a year’s work lay as scrap. The customer missed his delivery deadline.
Had the customer been willing to answer the lab’s questions, the lab would have developed the test he needed. A written spec could have alerted the lab’s engineers that the customer wished to subject his prototype to a 17-g peak acceleration with a duration of 100 ms. That’s commensurate with dropping the specimen from a 5-ft height; the MIL-S-901 tester’s hammer falling from 5 ft. delivered significantly more acceleration.
Working with a Lab
You are likely to need a test lab for one of two reasons: You need a laboratory’s quotation so you can include test costs as a line item in a proposal (see “Pricing Tests for Bid Purposes,”), or, more likely, you have a prototype or description of a new product that will require vibration testing. This second scenario invariably prompts the most questions from the lab engineers and technicians.
When you contact a laboratory, you can expect this sequence of events:
1. You’re referred to the lab’s quote department.
2. An engineer in that department discusses your testing requirements and assesses the lab’s ability to respond. He or she may consult others within the lab or introduce you to a test-department manager so you can discuss your needs.
3. You transmit a formal request for quote (RFQ). In cases where you are supplying to the government a product that requires testing under a CDRL (Contractural Deliverable Requirements List), your request letter can precede all other activity.
4. The quote department processes the RFQ and determines prices for each test, based on the required materials plus required engineering, technician, and machinist hours. The pricing normally includes developing procedures, preparing test fixtures, performing tests, and writing test reports.
5. Engineering management reviews the quote representative’s estimate.
6. The lab’s contracts department drafts a quotation letter, presenting the price by line item, an estimate of lead-time required prior to test, and the estimated test time.
7. You receive the quotation letter.
8. If the quotation is acceptable, you issue a purchase order. Once the purchase order is accepted by the contracts office, the work is assigned to a specific test engineer who will communicate with you throughout the execution of your test program.
Step 2 is where you’ll need to answer the most questions about your product and its test needs. You can expedite the process by preparing to answer the questions in “Eleven Useful Questions" before you contact the lab.
Usually, the test lab wants to learn why you are requesting a specific vibration test. Your reasons for wanting the test will help the lab develop a satisfactory test program. For example, your company may want to supply a product to the government directly or through a prime contractor, so you need to comply with the testing specifications of a CDRL. Or you face a CDRL-like situation, but without government involvement. (Many companies have adopted testing policies similar to those that government agencies impose.) In these cases, your contract with your customer should delineate the testing requirements, and you should share those requirements with the test lab.
You may want to conduct vibration tests because you want to characterize a new product, determine why excessive field failures have occurred, identify latent workmanship defects (such as bad solder joints, loose connections, and poor welds) by performing periodic environmental stress screening (ESS), or outsource vibration tests you typically perform in house. In these cases without customer specification, the key to satisfactory testing is to specify your requirements in detail. Before you deliver a test specimen to the lab, you must state the desired results and agree on the scope of work, schedule, report requirements, and other essentials.
Be sure to allocate enough time to clearly present your testing requirements and the intent of the needed test. Many questions should flow—in both directions. Since the time the customer allocates for testing is often compressed between the customer’s design and manufacturing phases, it is critical not to waste time with misunderstandings. With clear communications up front, you can avoid testing disappointments and disasters and get into production faster. T&MW
Wayne Tustinis president of Equipment Reliability Institute, Santa Barbara, CA.Rick Smithis manager of dynamics, andDan Reederis marketing manager at Wyle Laboratories, El Segundo, CA.
Pricing Tests for Bid Purposes
Suppose you're working on a proposal to secure a large contract to produce widgets. You know the contract will mandate testing, and you want to include commercial lab pricing as a line item in your proposal. Keep in mind that your competitors may ask the same lab you approach to provide test pricing for the same contract. Make sure the lab understands its obligation to maintain the confidentiality of each vendor and to provide consistent pricing to each vendor for the same effort. (The lab's quote department should flag requests for quotes that appear similar or identical.)
The key words here are "same effort". If you can suggest to the test lab a technical approach that reduces the level of effort required of the lab, the lab can offer you a lower price. In addition, it is obligated not to share information about your approach with the competing vendors.
Eleven Useful Questions
Be prepared to answer these 11 questions when you approach a test lab:
1. Is testing imminent (are specimens ready for test), or do you just need test pricing as part of a proposal package?
2. Does a complete test specification exist for this test? If so, provide it in its entirety to the testing laboratory. If you can only transmit a portion, make sure the portion includes all test tolerances and references to other documents.
3. Do you want the lab to prepare a test plan? If so, do you want the lab to quote the preparation as a deliverable line item or to amortize the test-plan-preparation cost within the total test cost?
4. How many test specimens do you want the lab to test, and when will you provide them?
5. Can you send a drawing of the test specimens? If not, can you provide specimen size (dimensions of the geometric envelope), weight, and interface information (mounting-point locations and fastener requirements)? This information will help the lab determine what fixture modifications it may require to accommodate your specimen.
6. Are you requesting a requote because of specification or scheduling changes? If so, reference the previous quote number.
7. Has this test been performed before at any facility (who, what, when, where, why, and how)? If the lab you’re approaching performed the test, provide the previous test-report number.
8. Who is your company’s contact for pricing information and for technical questions?
9. When is the quotation due?
10. When do you expect testing to start, and what is your deadline for test completion?
11. When do you need preliminary results, and when do you need a final report?