Philips齿轮模具标准

1、PhilipsPhilips齿轮模具标准34.SummarySummaryTo develop high precision products the HP Carriage Development” has been investigated The carriages are high precisi on pro ducts where PMF learned together with Hewlett-Packard to develop products that are capable for high precision in jection moulding. The tear

2、 rung asp ects are wrilten down in this report.The result of the investigation is a general description of design rules for high precision injection moulding that can be used in the early stage of product developmentThe earlier the cooperation can start the more efficient the product can be designed

3、 for high precision. Efficient in a way of smarter and faster.This report consists of:General theory of high precision in plasticsDescription of two carriages redesigned for attainable precision within CCP and now manufactured within the BG-Plastics in cooperation with HPSet of design rulesCase stud

4、y to show how to use the design rules.Design engineers can directly use the proposed set of design rules. The design rules are based on rules determined by the injection moulding process, rules determined by the polymer material, rules determined by the mould and rules determined by the functional r

5、equirements of the productThe case study helps to explain the total process of designing for high precision injection moulding, with help of the design rules.The producl design is essential for high precision injection moulding. A poorly designed part no matter how extraordinary the mould con struct

6、i on or pro cess is. can destroy any chance of achieving the very tight tolerances of the precision part3TableTable ofof ContentsContents1. Introduction2, Background2.1 Introduction2.2 Attainable tolerances and causes inaccuracies2.3 Influences on precision3, Hewlett-Packard3.1 Way of working3.2 HP

7、process system3.3 Co-operation with Philips4 Rogue4.1 Sp ecifications4.2 Development general4.3 Tolerance analysis4.4 Product Design4.5 Mould Design4.6 Material4.7 Process Design4.8 Design rules Rogue155 Carnegie5.1 Sp ecifications5.2 Development Carnegie general5.3 Tolerance analysis5.4 Product Des

8、ign5.5 Mould Design5.6 Material5.7 Process Design5.8 Design rules Carnegie276 Design rules6.1 Process6.2 Material6.3 Mould64 Product397, Case study7.1 Sp ecifications7.2 Product analysis7.3 Development7.4 Next generation478, Literature613AppApp endicesendicesApp endix AStatistic Process Control (in

9、Dutch)Appendix BInjection moulding and tolerances (in Dutch)Appendix ClProduct documentation RogueAppendix C2Tolerance analysis RogueAppendix DAttain able tolerancesAppendix ElProduct documentation CarnegieAppendix E2Tolerance Analysis Carnegie1.1. IntroductionIntroductionThis preject has been set u

10、p to fasten down the knowledge within the CCP about high precision injection moulding in relation to the Hewlett-Packard (HP) carriages. Two carriages for HP are developed for high precision injection moulding in cooperation with Philips Competence Centre Plastics,Rogue” was a lest case to develop a

11、 precision technology by injection moulding, fit for high precision in high volumes. In this case tolerances had to be attained, not by adjusting in the assembly line but by injection moulding. The results were the base for the development of the manufacturing process (part design, mould manufacturi

12、ng, injection moulding process) for the “Carnegie” carriage.With the goal to help HP in the future develop!ng products with similar aspects it is important to fasten down the obtained knowledge about this subject. This study will result in a general description of design rules for high precision inj

13、ection moulding that can be used in the early stage of development. The earlier the cooperation with the customer can start the more efficient the product can be designed for high precision. Efficient in terms of shorter lead-times and more robust processing.The goal of the design rules is to share

14、the knowledge within the BG-Plastics so people can use the experience in the future designs.This report starts with a general description about high precision injection moulding. Special attention needs to be paid to the process, the mould, the material and the product design. The product design is

15、essential for high precision injection moulding. A poorly designed part, no matter how extraordinary the mould construction or process is, can destroy any chance of achieving the very tight tolerances of the precision partThe carriages of HP are the exam pies used to finally formulate the design rul

16、es for high precision injection moulding. One chapter has been spent on the development of the Rogue and one on the development of the Carnegie. This report ends with a test product to illustrate the design rules.2.2. BackgroundBackground2J2J IntroductionIntroductionTalking about precision in plasti

17、cs, is talking about micrometers and how to control micrometers within specification. It is about precision of plastic parts without any finishing treatment, Precisi on is in flue need by;1,Material2,Process3,Mould4 Product designSo how can these aspects be handled to get the required precision? Bef

18、ore answering this question it is imp ortant to know what the inaccuracy sources can be and what the cap able precision of plastics is.What are attainable tolerances and what causes inaccuracies in the product?2.22.2 AttainableAttainable tolerancestolerances andand sourcessources ofof inaccuraciesin

19、accuraciesFour elements are related to high precision injection moulding. Each element has its own requirements in respect to material, process, mould and product design.1 Dimensional accuracyThe nominal values and their tolerances required for the product,2, Shape accuracyIn accuracy in the sha pe

20、like warp age and sink marks.3 ReproducibilityStability of dimensions and shape in mass manufacturing, Cp- and Cpk-values (appendix A). 4 Long term stabilityLong term stability of dimension and shape as function of time, inaccuracy caused by moisture absorption, ageing, creep etc.To deal accuracy of

21、 plastics in a good way, sources that can lead to inaccurate products have to be distinguished. Two types of variations in flue nee the accuracy, The irreversible variations, like shrinkage, volume relaxation, moulded in stress relaxation and after shrinkage. The reversible variations like expansion

22、 through variations in temperature and humidity, Separately from these sources related to the process and material there is a source of in accuracy directly related to the mould.During the process the plastic melt will become solid, which means a reduction of the specific volume. The material shrink

23、s and the final product dimensions are smaller than the mould dimensions. The mould has to be compensated for this effect.Plastics have the property that the shrinkage can not fully be influenced during the process and this causes a variation on the dimensions. If the variation is not time-dependent

24、 the process can be called stable. The p rocess is rep reducible and the p roducts are within an acce ptable process window. The shrinkage can partly be compensated with applying a holding pressure, extra material is postJilled into the cavity.Because of the cooling of plastic during the injection m

25、oulding process, thermal stresses will be induced in the materiak The volume will change, because the entropy of the material is not maximal and causes a time-dependent change of free volume. The plastic strives to equilibrium of the p ackage of its molecules, this is equal to an in crease of densit

26、y.With injection moulding the cooling time is much shorter than needed. The result is that the specific volume is not in equilibrium. For glassy polymers the free volume is too large. For semicrystalline polymers the crystallisation is not fully developed. Every thermo-dynamic system strives to maxi

27、mum entropy (equilibrium state) that means that in time there is a relaxation of volume (post-shrinkage or postcrystallisation) result!ng in a change of shape or dimensions. Although this aspect cannot be eliminated, it can be minimised by slower cooling (higher mould temperature). See appendix B.Ap

28、plying plastics means apply them in conditions that can change. All plastics will show dimensional variations under changing conditions. Variation in ternperature causes dimensional variations, the same for variations in humidity. Some plastics absorb water and swell Because the thermal expansion of

29、 plastics is mostly larger than metal, this is a point of attention when applying plastics in combination with metals.To design a product that can be produced with high precision you have to take in account the way tolerances are built up. The four aspects that influence the attainable precision hav

30、e their own contribution in the tolerance structure.The attainable tolerances can be divided in:1 Mould tolerances (mould)The total concept and the machining method that is applied determine the accuracy of the mould.2,Process tolerances (process, material)The plastic that is used determines the att

31、ainable tolerances. The properties that influence the accuracy of the product differ per plastic materia! type.3,Product tolerances (product design)The sum of the mould and the process tolerances is the minimal attainable toleranee (=Cp, cap ability of the p rocess). The p roduct n eeds to be design

32、ed with a very close relation to the process and the mould (=Cpk, capability of the process related to the product specifications).Within the PMF a tool has been designed to give the product designer more insight in attainable tolerances for plastic products and the attached price consequences. It i

33、s called “Attainable Tolerances in Plastics” and has also been used for the HP carriages projects. Five groups of materials (A, B, C, D, E) and three classes of accuracy (I, II, III) are distinguished. The combination of material A (most predictable accuracy) and class I for the mould/process has th

34、e best opportunities for an accurate product. It is also the most expensive one with the most difficult process.2.32.3 InfluencesInfluences onon precisionprecisionFor the definition of precision the classes of accuracy from called “Attainable Tolerances in Plastics” are used.IPrecise: adapted precis

35、ion moulds, technically optimal precessing conditions, intensive final inspection and high additional costs.IIAccurate: accurately dimensioned moulds, precessing controls less critical and moderate additional costs.IIINormal: mould tolerances can be obtained in normal procedures, the processing cond

36、itions are balanced to an as cheap as possible manufacturing process and normal additi onal costs.The feasible precision is influenced by:MaterialTaking the accuracy into account the choice of material is determined by the shrinkage and after shrinkage, the structure of the polymer amorphous or semi

37、-crystalline, the anisotropy of the shrinkage and expansion.Semi-crystalline therm op lastics shrink more during the cooling in the mould. Because of the control of shrinkage is proportional to the rate of shrinkage these materials have less potential for high accuracy, Amorphous plastics are better

38、 suitable for high precision. In general: products can better be designed for high precision when using material with a low shrinkage. Shape accuracy is strongly related to the same aspect. Differences in shrinkage within a part cause warp age. The larger the shrinkage is, the greater the rate of un

39、acce ptable deformati ons of the part.Filling the p lastic with glass or carbon reduces the shri nkage and guarantees pro ducts with better p recision. The material is stiffer and can reduce warp age. Because of the filling the material has a larger anisotropy caused by the orientation of the fibres

40、, which stimulates warp age. It seems better to use sp heres instead of fibres for the orientation effect, but in practice the differenee has never been demonstrated.The choice of material is not only based on high precision, other aspects like chemical resista nee, elasticity, temp erature range et

41、c, play an imp ortant role.ProcessThe plastic used determines which precessing tolerances can be adhered in the classes of accuracy. When the material choice has made the process has to be optimised for the plastic. Operating an injection moulding process means controlling several important paramete

42、rs. Realising a product according to tight specifications means an extensive investigation into the in fluences of each p rocess parameterMain parameters are:Filling stage (injection time, injection speed, injection pressure)Cavity pressure (holding pressure, holding pressure time)Cavity temperature

43、 (mould temperature, cooling time)Melt ternperature (cylinder zone temperature)These parameters are used for better controlling the shrinkage.The effect of the holding pressure is that the thermal volume shrinkage is partly compensated, so that the shrinkage is better controlled. This means more pre

44、dictable dimensions and shape and less thermal stresses.HP executes an injection moulding optimisation to determine the process window according to a prescribed procedure. The process has to be robust. A robust process has a process windowthat includes all not con trolled variati ons of the p rocess

45、, A p rocess variation within the process window will not cause out of spec parts (See chapter 3- HP Process System).MouldPrecision in respect to the mould exists of two aspects, the tolerance of the assembled inserts to each other and the toleranee on the manufactured inserts itself. The dimension

46、of the tolerance of the assembled inserts to each other is determined by the centring of both mould halves, the amount of slides and the inaccuracy of inserts. The attainable class of accuracy is thus limited by the machining method. Grin ding is more accurate than milling for example. Table 2,1 sho

47、ws the cap abilities for several machining methods.dimensionmethod ( most accurate)jig-grinding (II)pro (1)spark erosion (II)copy milling (III)10 mm0.0050.0040.0030.016100 mm0.010.0060.0050.022Tolerance ( mm) With special precautions and extra cost tighter tolerances are achievable, Max 1 gmTable 2J

48、 Attainable tolerances manufacturing (Source: Attainable Tolerances, Anemaat)Tool bounded dimensions are realised in one half of the mould, not tool bounded dimensions are dimensions that are not realised in one of the halves of the mould, but are realised through various moving parts of the mould.

49、For not tool-bounded dimensions the attainable tolerance has to be increased with 25 gm.The class of accuracy of the mould is determined by the most accurate dimension of a product. The largest source of inaccuracy is caused by the margin for shrinkage applied on the mould to com pen sate the differ

50、ence between the mould dimensi ons and the p roduct dimensi ons. For precision class I the predictability of the shrinkage is not sufficient enough, so the mould has to be corrected on functional dimensions based on the results of the trial runs. For high precision moulds it is important to have the

51、 possibility to modify the mould-dimensions steel safe, that means removing steel instead of adding.Product designThe product design has to be made in close relation with the material choice, process conditions and the mould design are already made. Design of high precision products is an iterative

52、process with an interactive character. It is not possible to design the product without taking into account the influences of the materiaL process and the mould on the accuracy of the final product.A large influe nee on the accuracy of the product and therefor on the p roduct desig n is the shape of

53、 the product. Dimensional accuracy needs to be disconnected from shape deviation, because it is more difficult to control the sha pe or warp age.The larger the nominal dimension, the more important the right estimation of shrinkage is to minimise the correction of the mould. Precision moulds just ha

54、ve their advantages for small p roducts.In general: if you use the design tools for high precision injection moulding smart, it is not always the more accurate the more expensive. It starts with a smart product design.Procedures:1 StartObjectiveMethodResult:Obtain the lowest pressure drop over the f

55、low path and thus the lowest flow- induced shear stress, by changing the velocity,:Fill the product with 90% plastic and vary the injection velocity; measure pressure drop in hotrunner. Use datasheet material supplier to determine the average mould temperature and average melt temperature. The injec

56、tion velocity with the lowest pressure drop is the most interesting.:Determination of injection velocityObjective Method3.3. Hewlett-PackardHewlett-Packard3.13.1 WayWay ofof workingworkingHewlett-Packard is an American company specialised in electronic equipment. They have a strong division for deve

57、lopment and innovation spread around the world. The manufacturing of parts is not an activity they do themselves. HP assembles the parts to finished products and put their strong brand name on it. For manufacturing and co-development they have partners to develop in an efficient way (win-win situati

58、on) new products. For the carriages of inkjet printers PMF is a partner for co-development and manufacturing.For high precision injection moulded products, HP distinguishes several stages in developing the new process. They start with test tools to prove the technology. Then they manufacture a proto

59、type tool, to test the feasibility of the functional part and to modify the concept for massproduction, This is an investigation of the functionality of the part. In the prototype tool, several op timising steps (devel op me nt steps) are p lanned. The lead-time per step is 6 weeks. After releasing

60、the process, preduction tools are manufactured and released in strict procedure.It ts better to invest in tools in the pre-stage of development, because it costs more money and time to modify the final production tool than the prototype tools.3.23.2 HPHP ProcessProcess SystemSystemThe basic idea beh