Choosing the right equipment
This is based on a document written by Dr. Patrick Collins Mecmesin's Technical Manager, and it provides some tips on the considerations that should be made before beginning any test regime.
Quality Control Test Considerations
How to choose the right equipment?
The testing phase is an essential part of a manufacturers' quality control program, and should obviously be initiated before a product ever reaches an end-user. A poorly designed product by impeding customers from effectively using or operating the product, can seriously damage a brands reputation resulting in a negative impact on profit margins.
This is why in-depth knowledge of key material characteristics is crucial in the development and continued production of high quality goods, saving time and money. By deciding to make test measurements and deciding buying the necessary equipment, it is important to make a qualified judgment.
To make this judgment easier and allow the initialization of a testing phase without problems, it’s necessary to consider the following 5 points: the objectives, the test, the product to be tested, the test environment and the test equipment
1. The objectives
It’s necessary to begin with a set of clear objectives. Without a defined target, it is difficult to identify valuable measurements and can lead to false conclusions, making the whole exercise costly and useless.
There are a few basic questions that should be answered at this stage, before compromising any time or budget:
- What product characteristics are of interest?
- What test or tests need to be performed in order to adequately determine these characteristics (tension, compression, torque)?
- What are the key measurements to find e.g. peak force, average force, force after an elapsed time-frame or at a precise angle of displacement?
- Does the test fall under specific compliance requirements? And, if so, is there a defined test method that needs to be adopted?
2. The test
Test criteria can be used to filter inadequate test equipment, by narrowing the selection those that can perform accordingly.
Some questions that you should consider at this point:
- Is there an acceptable tolerance level with which to establish pass/fail criteria?
- What is the anticipated maximum load?
- Does the test require a single-stroke, multiple strokes or many cycles? If multiple cycles are required, how many are needed and what data needs to be collected?
- Will the test trigger an 'event', e.g. a break in the sample? Does this need to be recorded?
- What speed, or speed range, does the test require?
- Does the test equipment need to interface with other factory equipment, such as a PLC, footswitch or SPC system?
3. The product to be tested
It’s necessary to consider the product to be tested and try to anticipate any problem that might arise:
- What is its shape and size?
- What is its orientation in the test machine?
- Will it need specially designed fixtures to accommodate its geometry?
- How many different types of sample will be tested, and are any of their test measurements incompatible?
- Could the sample stretch beyond the limits of a standard tester, in which case, will it be necessary to have a custom built model made?
- Are there any particular product attributes to consider before beginning any test measurements?
- Is there a risk the sample could shatter or escape from the fixture during testing, causing potential injury, or does the sample require protection from the test environment? If so, then a guard may be necessary.
4. The test environment
The test area needs to be prepared. This avoids unnecessary moving of the equipment, especially when dealing with heavy equipment.
These are the questions to ask at this stage:
- Where will the test equipment be placed?
- Is there enough space to accommodate the equipment (width, height)?
- Is the work surface stable and able to cope with the weight of the system?
- Does the test system need to be securely bolted down onto the work surface?
- Are there any environmental aspects that might affect results?
5. The test equipment
When selecting the test equipment it’s necessary to think carefully about the system requirements. Under specification can be detrimental to test outcomes, but over specification can be expensive and unnecessary.
Accuracy and repeatability are key factors and need careful consideration. It is also necessary to take into account the operator of the equipment and his/her competence to operate the machinery and set up each test consistently.
Depending on the degree of sophistication and advanced features required, the test solution options fall under the following categories: handheld, manual testers, motorized test equipment, console/touch screen test equipment, computer–controlled test equipment..
Devices that are easy to use and are portable. They can be used for tests that need to be performed in situ.
As a disadvantage, there’s a greater risk of obtaining inconsistent results..
5.2. Manual testers
These devices (Ex.: lever-operated and handwheel-operated) enable the application of manual low-level forces/torques. Simplicity and portability are once again their great advantage, enabling quick elementary tests to check basic performance attributes. They are cost-effective and versatile solutions.
However, the cross-head speed will depend on the operator, so tests are less repeatable when compared to motorized systems
5.3. Motorized equipament
They allow for higher testing capacities. They improve accuracy, reproducibility and repeatability when compared to the manual devices because of the constant speed rate at which measurements are made.
These systems are optimized with a digital force gauge to allow repeatable and consistent force measurements. This gauge interchangeability also allows greater flexibility. Often used within production areas for speed and accuracy..
5.4. Console/ touch screen test equipment
These are semi-automated and can be programmed by the user, they offer greater versatility in comparison with basic motorized systems.
They are ideal for places where a PC based system is not appropriate, such as the production environment, but more sophisticated testing is required. They are easily programmable and provide quick, accurate test measurements with traceable results to International test standards.
5.5. Computer controlled test equipment
Other things to bear in mind when choosing the test equipment are the transducer capacity and the accessories.
They offer users full control over test design and subsequent evaluation and reporting requirements. This means operators utilize dedicated software, installed on a remote PC, to program tests to their exact specifications, which can include fully automated cyclic testing and tolerance alerting, etc. Results are presented graphically on the screen and a detailed account of each measurement can be shown.
The benefit to running on a PC platform can be taken advantage to exporting to Excel, Word or other PC software, etc..
It’s necessary to analyze the requirements and to be sure to choose the necessary load cells or torque sensors to satisfy those same requirements with sufficient headroom that doesn’t overload the load cells, but not so much that compromises sensitivity. A good rule to consider with these is the fact that their performance is optimal between 10% and 90% of their capacity. About the most appropriate capacity, it’s always better to ask the advice of a test expert.
A wide range of standard grips and fixtures are ready to perform the most common tests. When the samples have irregular forms or geometry, it’s possible to request a specially made accessory, guaranteeing that the sample is properly placed for the test.
Before the selection of the accessories or grips, it’s crucial to answer the following questions:
- Tension, compression or torque? Does the test require a push, pull or turning accessory, or perhaps a combination of accessories to perform a variety of tests?
- Can the sample be gripped using a standard fixture or does it require a unique accessory in order for the sample to be held correctly?
- What is the size and material of the specimen?
Other things to consider are about the grip face, if it’s too wide or narrow or even if it’s too tight, the contact with the sample might be uneven and consequently stressful. Usually tests are about the force required to break a material at its weakest point, but if the sample is stressed by the grip then it is more likely to break at a point determined by the grip and not by the material.
Force and torque measurement is essential in quantifying the functionality and usability of products. The considerations here stated help with assessing the requirements, choosing the equipment and they consequently ease the testing process. The outcome should be a well specified test solution that meets your current and future requirements; a solution that performs accurate and repeatable force and torque test measurements for your quality control needs.
However, it is worth to note that no matter what equipment you buy, the most important thing is to design your test / test sequence correctly. A well designed test on a simple and cheap equipment may produce more meaningful data in compassion to a badly designed test, performed on a more advance and expensive equipment.