【正文】 different types of wires, at different temperatures and cutting feedrates. Keywords: polystyrene, surface form, hotwire 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 foams. 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 and 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 installation. The production of foams can take place using many different techniques. The most mon method to produce continuous foam slab is by pouring mixed ingredients of petrochemical agents that include toluene diisocyanate, polyol and water. These ingredients are left to rise and cure. Additives 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 materials, which are by using hotwire 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 hotwire technique is capable of producing plicated geometrical shapes and is suitable for flexible foams. Presently, both techniques are performed either manually or in a semiautomated 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 research for determining the surface form of polystyrene. A CMM consists of a probe to measure points on a workpiece. 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 workpiece. Each point on the workpiece is unique to the machine’s 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 called the part coordinate system, where the three axes relate to the datum of the workpiece. A datum is a location of a feature on a workpiece. It can be a hole, a surface or a slot. A CMM measures a workpiece to determine the distance from one feature to another. It can also be used to determine 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 D12 (Fig. 1a).Data are gathered by touching the test piece with either a solid probe or an electronic touch trigger probe. This 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 , , , and in diameter. The stylus used in this experiment was ruby with a size of 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 polystyrene. Therefore, the stylus 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. This 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 pe