1、 附录 Determining the surface form of polystyrene through the coordinate measurement machine D Aitchison and R Sulaiman* Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand Abstract: The market for foam materials has been growing rapidly throughout the world as th
2、ey have a variety of uses. Some examples are in the automotives industries, food packaging industries, medical application, sports gears, home insulations and floatation in offshore drilling rigs, buoys and small boats. Since the uses of foam affects greatly the daily lives of humans, the need to ha
3、ve foams in different shapes requires speed in cutting and manufacture. This can only be done through computer aided cutting machines or automated cutting of foams. However, the speed of cutting will affect the surface . finish of the cut. Therefore, it is necessary to determine the surface form of
4、the polystyrene to achieve quality results. This is an on-going research to produce a rapid-prototyping machine that cuts foam models. The . first phase of this research is to determine the surface form of polystyrene through the use of a coordinate measuring machine (CMM), after being cut with diff
5、erent types of wires, at different temperatures and cutting feed-rates. Keywords: polystyrene, surface form, hot-wire cutting 1 INTRODUCTION The market for foam material has been growing rapidly throughout the world. Foams can be categorized into two major types, namely flexible foams and rigid foam
6、s. The flexible foams are mainly used in furniture, transportation, bedding, carpet underlay, packaging, toys, sports application and shoes, as well as for vibration and sound attenuation. The rigid foams are usually used in building appliances, insulation agents, pipes, tanks, floatation and food a
7、nd drink containers 1. The reason why foams are used everywhere can be summarized as follows: 1. Foam is very inexpensive. 2. Foam is suitable for use indoors or outdoors. 3. Foam can be coated with many different products to achieve any desired . finish. 4. Foam is lightweight for easy handling and
8、 installation. The production of foams can take place using many different techniques. The most common method to produce continuous foam slab is by pouring mixed ingredients of petrochemical agents that include toluene di-isocyanate, polyol and water. These ingredients are left to rise and cure. Add
9、itives are blended in for specific. characteristics such as colors, absorbing capacity, effects on ultra violet and others. This method produces foam in its raw state, which must then be formed into different shapes and sizes. This is usually done by cutting the foams. There are two ways to cut foam
10、 materials, which are by using hot-wire techniques and the oscillating blade method. Both produce different features to the foams. The oscillating blade produces simple geometrical shapes and is suitable for rigid foams. The hot-wire technique is capable of producing complicated geometrical shapes a
11、nd is suitable for flexible foams. Presently, both techniques are performed either manually or in a semi-automated manner 2. 2 COORDINATE MEASUREMENT MACHINE (CMM) Before further discussion, it is necessary to describe the features of a coordinate measurement machine (CMM) as a tool used in this res
12、earch for determining the surface form of polystyrene. A CMM consists of a probe to measure points on a work-piece. This is similar to using a . finger to trace a map coordinate. The probe acts as a . finger that points or touches a certain location on the work-piece. Each point on the work-piece is
13、 unique to the machines coordinate system. The coordinate system describes the movement of the measurement machine. There are two types of coordinate system. The . first is called the machine coordinate system. Here, the X, Y and Z axes refer to the machine s motion. The second coordinate system is
14、called the part coordinate system, where the three axes relate to the datum of the work-piece. A datum is a location of a feature on a work-piece. It can be a hole, a surface or a slot. A CMM measures a work-piece to determine the distance from one feature to another. It can also be used to determin
15、e the form or roughness on a surface of a soft object, such as polystyrene. The CMM used in the present experiment is the Discovery Series coordinate measuring machine Model D-12 (Fig. 1a).Data are gathered by touching the test piece with either a solid probe or an electronic touch trigger probe. Th
16、is experiment uses the electronic touch trigger probe. The probe measurement was taken perpendicular to the test piece to obtain the optimal result because probe tip skidding will affect the reading of data. The stylus sizes that are available in the authors laboratory are 1.0, 2.0, 3.0, 4.0 and 5.0
17、mm in diameter. The stylus used in this experiment was ruby with a size of 3.0mm in diameter. As polystyrene is soft, a smaller stylus size may create new slopes or holes when touching the polystyrene (Fig. 1b). A larger stylus size may not detect the existing slopes and holes on the surface of the
18、polystyrene. Therefore, the stylus 3.0mm in diameter was used to avoid the above reading errors (Figs 1c and d). 3 SURFACE FORM It is generally agreed that surface form or roughness consists of scratch marks and fragmentation marks within them. These marks are relatively closely spaced together. Thi
19、s makes them dif. cult to measure. Why do engineers trouble to measure surface roughness at all? The main reason is that the surface being measured will be in contact with some other surfaces. By understanding its surface, the nature of the contact and the performance of the contacted components can
20、 be controlled. （ d） Fig. 1 (a) The CMM used in this experiment； (b) the surface of polystyrene as seen through a microscope； (c) typical diagram of the probe； (d) the probe used in this experiment It is necessary to state that surface form and surface roughness are not the same. Surface form is a g
21、eometrical pro. le of a surface on soft materials, such as polystyrene or sponge. Measuring surface roughness on soft material is challenging and complicated, but can be done 3. Surface roughness is more commonly recognized as an irregular or uneven surface, usually on hard materials 4. The definiti
22、ons tend to refer to the technique or scale of measuring its hardness. If surface roughness needs to comply with a written standard, there are a few to choose from. The most common is the British Standards Institution BS 1134, Centre-line Average Height Method for Assessment of Surface Texture, 1961
23、. There is also another one being used in the mechanical engineering industry to date, which is the International Standard ISO 4287, Surface RoughnessTerminologyPart 1Surface and Its Parameters, 1st edition, 1984, pp. 1215. The measurement standards are based on a line pro. le obtained by scanning a
24、 mechanical stylus across the surface. For a thorough assessment of the roughness standards, refer to ISO 4287 and the published national standards based on this ISO documents. The latter can be traced by contacting national reference laboratories, e.g.National Physical Laboratory in the United King
25、dom, Physikalishe Technishe Bundesanstalt in Germany, National Institute of Standards and Technology in the United States and Laboratoire National dEssais in France. 4 SURFACE FORM FOR SOFT MATERIALS Questions are often raised concerning the possibility of measuring surface roughness of soft materia
26、ls such as polystyrene or other foam materials. A suitable method of measuring is by using the optical technique. However, with the optical technique careful attention must be focused on local, steep slopes in the surface of the test piece, as the dynamic focusing instruments tend to produce corrupt
27、 feedback at these points. Other optical techniques encounter problems with steep local slopes by not reflecting enough light back into the detector system. This is the main reason why this research uses the CMM machine. The CMM machine can measure the surface form of polystyrene because polystyrene
28、 usually does not have steep slopes. When examined through a microscope, these slopes appear to be sperical in shape. Results of the tests are produced as shown in Fig. 2. Notice that the deeper the slope, the longer the line produced by CMM readings. 5 EXPERIMENTAL TECHNIQUE In this research, a sim
29、ple machine is designed to cut polystyrene using the hot-wire technique. The machine will cut the polystyrene in a one-dimensional movement, i.e. feeding the hot wire horizontally towards the polystyrene. Hot-wire foam cutters are very common when working with polystyrene. The two ends of the hot wire are connected to a power source. Heat will flow when
