Manufacturing engineering tests are essential to ensure the quality, performance, and reliability of products and processes. They help to identify and correct defects, optimize designs, and validate specifications. In this article, we will explain how to perform some common manufacturing engineering tests, such as tensile, fatigue, hardness, and dimensional tests.
A tensile test measures how a material reacts to being pulled apart by applying a controlled force. It can reveal the strength, elasticity, ductility, and fracture behavior of the material. To perform a tensile test, you need a tensile testing machine, a specimen with a standardized shape and size, and a device to measure the strain. You attach the specimen to the machine and apply a gradually increasing force until the specimen breaks or deforms. You record the force and the strain at each stage and plot them on a stress-strain curve. You can calculate various properties from the curve, such as the modulus of elasticity, the yield strength, the ultimate tensile strength, and the elongation.
Tensile testing has a broad range of applications to include assessing shifts in material performance over defined time points (for plastics) as well as determining the weak points in a design with multiple potential failure locations. Tensile testing is pull rate sensitive and rate speed should be established based on applicable standards for the subject material and functional application or after completion of internal studies.
Tensile strength is a measure of a material's ability to withstand a pulling force without breaking or deforming. It indicates the maximum amount of tensile (stretching) stress a material can endure before failing. This property is crucial in engineering and materials science, helping to determine the suitability of materials for various applications. Tensile strength is often reported in units of force per unit area, such as pounds per square inch (psi) or megapascals (MPa). Different materials exhibit different tensile strengths due to variations in their atomic and molecular structures.
We apply this test mostly for adhesive to determine if meets specification and if not is there some way to pre-treat the material.
The machine called to measure tensile strenth is UTM. Tensile strength basically measure along axial direction of specimen or product where tensile stress to occurs. any formation of notch or step it affects stress concentration and changes tensile stress of product.
Factors to be considered while performing the tests are 1. Consider the temperature conditions of the pieces under test and the sample size 2. Check and verify the calibration status of the test equipment if it meets requirements.
A fatigue test measures how a material withstands repeated or cyclic loading over time. It can reveal the endurance limit, the fatigue life, and the fatigue strength of the material. To perform a fatigue test, you need a fatigue testing machine, a specimen with a standardized shape and size, and a device to measure the stress or strain. You subject the specimen to a cyclic load with a specified frequency, amplitude, and waveform. You record the number of cycles until the specimen fails or reaches a predetermined level of damage. You plot the stress or strain versus the number of cycles on a S-N curve or an ε-N curve. You can determine the fatigue properties from the curve, such as the fatigue limit, the fatigue ratio, and the fatigue crack growth rate.
I would consider fatigue test more of reliability engineering. I would apply this fatigue test more to work hardening effect in assembly process.
Material fatigue is a phenomenon that occurs when a material undergoes repeated cycles of stress and strain, leading to its gradual degradation and eventual failure, even if the applied stress is well below its maximum strength. This process can result in cracks, fractures, and other structural weaknesses in the material. Common in industries like aviation, automotive, and manufacturing, material fatigue is influenced by factors like cyclic loading, temperature changes, and corrosion. Engineers and designers take fatigue into account when creating structures and components, using techniques such as stress analysis and fatigue testing to ensure product durability and safety.
For a complete analysis of part resource. It is necessary to carry out fatigue tests of the parts themselves, and not just the material. So the design of the parts greatly affects the strength. So it would be nice to imitate the working conditions of these parts. Since there are always static and thermal loads. Also, parts have several resonant frequencies and, accordingly, vibration modes. And on different forms, the places of maxima are in different places. Great difficulties arise during fatigue testing of parts at frequencies above 10 kHz.
A hardness test measures how a material resists indentation or penetration by applying a fixed load with a specified indenter. It can reveal the resistance to wear, abrasion, deformation, and plasticity of the material. To perform a hardness test, you need a hardness tester, a specimen with a smooth and flat surface, and a device to measure the depth or area of the indentation. You press the indenter into the specimen with a known load for a specified duration. You measure the depth or area of the indentation and compare it with a standard scale. You can report the hardness value in different units, such as Brinell, Rockwell, Vickers, or Knoop.
A durometer scale is used for elastomeric and plastic materials introduced or implanted into the body as a measure of material compliance.
When using Rockwell hardness, conical diamonds provide the best result for steel alloys. This means the material has undergone heat treatment to value this measurement.
Rockwell hardness also uses a minor load as well as a major load. The hardness number is generated by the distance of penetration between minor and major loads.
A dimensional test measures how a product or a part conforms to the specified dimensions, tolerances, and geometries. It can reveal the accuracy, precision, and consistency of the product or part. To perform a dimensional test, you need a measuring instrument, such as a caliper, a micrometer, a gauge, or a coordinate measuring machine. You measure the relevant features of the product or part, such as length, width, height, diameter, angle, or radius. You compare the measured values with the specified values and calculate the deviation or error. You can report the dimensional test results in different formats, such as a dimensional inspection report, a first article inspection report, or a certificate of conformance.
All parts require dimensional control, but the specification limits have to be reasonable. And as always check you stack-ups to insure you are including the total assembly
Even though the CNC machining is controlled by NC program, 100% dimensions need to be verified for the first part. It is usually called "first off inspection" and it validates the setup. So it is also called setup validation
When holding tight dimensional tolerances in die cast machining applications there are often many factors to consider. Machine repeatability and thermal stability, coolant temperature control and environment temperature control. If you find yourself chasing dimension repeatability you may need to start isolating these factors and controlling for each.
In addition to an FAI, it can be beneficial to do a capability study to validate the repeatability of a process. An FAI tells you you can make the part per print. The study says you have control of tool, wear, machine anomalies, etc...
Make sure you are interpreting the dimensions and tolerances specified on the drawing correctly. Familiarize yourself with the GD&T spec called out on the drawing. In most cases, GD&T Rule#1 will apply. Pick your measuring instruments accordingly.
One of the areas I would like to mention would be risk mitigation. Sometimes reducing risk may include other tools like PFMEA to identify risk you may overlooked.
Train your team to be able to run a given process with as much up-skilling as possible. This will maximize both run time and quality while demonstrating that you have an interest in providing growth opportunities for your team.
DOE .- also known as experiment design or experimental design, is the design of any task that aims to describe and explain the variation of information under conditions that are hypothesized to reflect the variation. The term is generally associated with experiments in which the design introduces conditions that directly affect the variation, but may also refer to the design of quasi-experiments, in which natural conditions that influence the variation are selected for observation. DOE is a powerful data collection and analysis tool that can be used in a variety of experimental situation or tests.
Microstructure testing is a process used to examine the internal structure and composition of materials at a microscopic level. It involves the preparation of specimens and their subsequent observation under a microscope or through other imaging techniques. The purpose of microstructure testing is to evaluate the grain size, morphology, distribution of phases, and other features within a material, which can provide valuable information about its mechanical, physical, and chemical properties. This type of testing is commonly used in metallurgy, material science, engineering, and other industries to assess the quality, integrity, and performance of materials.
APQP, or Advanced Product Quality Planning has many benefits with manufacturing risk reduction. A well thought out and documented PFMEA can I agree, be an invaluable tool as part of that process. The use of control plans coupled with the PFMA, helps get the risk reduction opportunities, at the point of manufacture and off the PFMEA document.