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General Information for how to polish instrument panels mould
Mainly hand-held devices are used in precision machining of surfaces in automotive instrument panels mould making. In many cases, this still represents a more economical way of working, especially when staff is well trained and the polishing work station is well equipped. In the series production, and for simple surface geometries and low surface qualities, however, automated polishing processes can be used and a suitable quality can be achieved.
Definition of the instrument panels mould Surface Roughness
Surface roughness is a term for defining instrument panels mould surface qualities. At least two criteria are needed to evaluate the surface of a mold insert.
- the accuracy of the geometry of a instrument panels surface is assessed, i.e., radii and flatness are checked for accuracy and are measured.
- the quality of the polish is assessed, which can be determined by measuring the instrument panels surface roughness. The polish is often diminished by polishing defects such as scratches, holes, pores, pinholes, and the orange skin effect.
The most common characteristics for the surface roughness are：
- Ra as the arithmetic mean of the deviations of the roughness from the midline,
- Rz is the average from the peak to valley distance of five individual sampling lengths,
- Rmax is the largest individual roughness within the evaluation length,
- Rt is the largest difference in height between peak and valley of the evaluation length.
All values can be determined, for example, with the aid of surface roughness test instruments by scanning the surface. (According to the new nomenclature, surface roughness can be defined with the characteristic value RmaX. In order to meet the accuracy requirements in steel mold making, Rmax should be used to its advantage.)
Systematic instrument panels mould Polishing Technique
Good surfaces can only be achieved through the application of logically consecutive processes, which always leads to smaller and smaller surface roughness.
- 1. Flat surface through: milling, grinding, lapping, polish lapping, polishing;
- 2. Cylindrical external surfaces through: turning, grinding, lapping, polish lapping, polishing;
- 3. Cylindrical internal surfaces through: drilling, reaming, fine boring, honing, lapping, polish lapping, polishing.
Taking out some machining processes, it can be said that the achievable instrument panels mould surface qualities are limited for each procedure. The left-sided wedge-shaped outlet of the bars means that better quality and lower surface roughness can be achieved under special conditions with most procedures. Although the slightest roughness depths can be created with today’s techniques such as erosion or when working with high-frequency spindles, rules of a polishing progress still remain in force. The only consequence： today, in contrast to earlier, a finer granularity is used for starting the precision machining process.
It must however be kept in mind that the hardness and microstructure of the steel or metal surfaces to be machined are to be considered, especially if high surface quality has to be achieved.
instrument panels mould Polishing Behavior-Influencing Factors
The polishability of various grades of automotive instrument panels mould steel is usually dependent on nonmetallic inclusions that negatively affect the quality of the polish due to hardness differences. Especially the hard oxides, but also the carbides which break out while polishing, lead to a poor surface quality. The selection of the automotive instrument panels mould steel is thus a decisive factor for the quality of the polish. Therefore, materials which are manufactured in special re-melting and degassing or sintering processes, and thus have good homogeneity, high purity, and low degree of segregation, are increasingly used.
The automotive instrument panels surface quality improves with increasing material hardness. To facilitate the machining, however, soft annealed steels are used.
In this state, the ferritic structure component is disturbend when processing. The ferrite, which is as soft as copper, sits firmly in the roughness of the blades resulting in built-up edges； an effect that occurs even with files with added chip spaces.
When machining steel, it should not be forgotten that a processing of the crystals in the structure takes place, i.e., the crystals are cut, shaped, and polished. Therefore, the principle cannot be invalidated that unevenness of a surface increases the longer a soft tool will be used.
Although more accurate surface geometries can be produced with machine processing, only limited roughness values are attainable. Accordingly, the selection of sequential machining processes has to be made.