2.7 Accuracy in Design and Manufacture Flashcards
(31 cards)
Why is accuracy essential to design, manufacture and test products?
Accuracy is essential in order to design, manufacture and test products within tolerance specified so that they will function effectively. This can only be achieved by the correct use of appropriate measuring and marking out tools. Additional equipment is also used to reduce the possibility of measuring and marking out errors, particularly in large-scale production.
What is meant by measurement?
It is the process of using tools such as rules, tapes and gauges to check existing dimensions.
What is meant by marking out?
It is the transfer of designs onto pieces of material or parts to indicate where features such as edges, holes, slots and recesses and bend have to be made during manufacturing processes.
How do you mark metal?
Marking metal requires the use of a high carbon steel scriber, which is harder than the metal it is marking, so it is able to scratch the surface. If the scratched lines are difficult to see, it is common for special ink such as engineer’s blue to be applied to the surface being marked out, so that the lines are more visible.
How do you mark circles or arcs onto metal?
If circles or arcs are required, dividers are used, which have 2 points and function the same way as a pair of compasses. Beam compasses, sometimes called trammels, can be sed for larger radii.
How do you mark timber?
It is usually marked out with a marking knife or pencil, and there are carpenter’s pencils specially designed for the purpose, with a thicker lead to avoid breakages.
How do you mark polymer?
A marker pen is usually used on a polymer sheet, although a scriber is sometimes used if the material is to be cut rather than bent.
How are laser devices used to mark out materials?
Laser devices such as cross line levels are becoming more commonly used for measuring and marking out when large and complicated fabrications are being undertaken, as this method projects a perfectly horizontal and vertical reference line onto objects of any shape.
What tools are used for marking out in engineering applications?
Surface plates and gauges fitted with digital or dial readouts, angles plates and v-blocks are often used when accurate measurement and marking out are required in engineering applications. For this type of work, it is necessary to establish datum surfaces, so that measurements can be accurately referenced from them, in the same way that a face side and edge are marked on timber to ensure squareness.
What is a marking gauge used for?
A marking gauge can be used to mark a line at a constant distance from an edge of a piece of timber.
How do you mark out holes for drilling?
When marking out holes for drilling, it is normal practice to use a centre punch mark to ensure that the drill centres itself correctly and does not wander.
What are some tools that are used for precise measurement involving fine tolerances?
micrometers, vernier calipers and co-ordinate measuring machines (CMMs)
What does a digital test gauge do?
The digital test gauge is a single axis measuring device that is used extensively for precise measurement. It has largely taken over the role of the mechanical dial indicator because it has the advantage of an easy to read display and the potential for providing direct input to computer systems.
At the manufacturing stage of products, why are dials fitted to the handles of machines with regard to accuracy?
The dials fitted to the handles of machines facilitate direct input in measurements for machining operations such as milling and turning. These graduated dials indicate the precise linear movement of the tools or workpiece for each revolution or fraction of a revolution of the handle, and can typically achieve an accuracy of 0.01mm, which is the linear distance travelled by the slide for one graduation rotation of the dial. The dial can be set to 0 at the start of the cut so that the distance moved can easily be gauged, although care needs to be taken when using a lathe cross slide to check whether the dial is calibrated for diameter or radius.
How is marking out materials linked to the use of CNC machining?
CNC machining processes don’t require marking out since the G-codes generated by the CAD/CAM software v=control the co-ordinate of the path of the cutting tool in relation to the workpiece. It is, however, necessary to ensure that the optimum layout for all of the parts has been established to avoid wasting material. This applied to all situations where decisions must be made regarding the optimum size of components in relation to stock forms of material that are available.
What is the definition of accuracy?
The level of conformity of measurement to the required value
Why is accuracy of components so important?
It is an increasingly important feature of modern product design to ensure that parts fit and products function correctly, particularly in light of more prevalent miniturisation of many devices.
What does it mean by tolerance/
The measure of the level of accuracy for particular situations, which can vary considerably depending on factors such as material, size, function and need for interchangeability.
How are tolerances expressed in measurements on components?
X+- Y, where X is the exact size required and Y is how much error can be tolerated.
What happens to components to components that outside of the tolerances?
They have to be rejected as part of the QA and QC measures
What does GD&T stand for?
Geometric dimensioning and tolerancing
What is geometric dimensioning and tolerancing?
The system normally used by designers and manufacturers to specify the required dimensions of a part or product
What is geometric dimensioning and tolerancing used for?
This is a standardised system of symbols and figures used on CAD model or engineering drawings that express the ideal distance and angular dimensions requires, along with the amount of variation that is allowable.
What tools can be used to improve accuracy, speed and eliminate human errors?
jigs, fixtures and templates
