Chapter 7 Design of Manufacturing Processes

Transcription

1 Chapter 7 Design f Manufacturing Prcesses General Cncepts: Design f the prcess (es) t prduce prduct shuld be cnsidered the primary activity ver all ther activities perfrmed by the manufacturer. Parts that are assembled int prduct shuld be: Made ecnmically Of gd quality On time Shing states: Prductin is a netwrk f prcesses and peratins Prcess transfrms material int prduct thrugh a series f peratins Prcess shws the flw f material in time and space Raw material =>semi-prcessed cmpnent =>finished prduct Operatins are wrk perfrmed t accmplish the transfrmatin Design f manufacturing prcesses is nt restricted t new firms r new prducts. Manufacturers are cntinuusly reviewing their peratins t increase prductin at lwer manufacturing csts Intrductin f new prducts Prduct imprvements Mdel changes Firms must have adequate rganizatin and prcedures t prvide fr planning f manufacturing methds. Many techniques and prcedures are invlved: Methds engineering Plant layut Prduct designer and prcess engineer shuld cllabrate n the design f the part r prduct T ensure material specificatins are met T ensure quality specificatins are met Designed t be prduced by the mst ecnmical methd Example: - Cncurrent engineering - Design fr assembly Prcess Design Scpe: Generally Prcess design planning begins with develpment f the prduct specificatins and ends with the final plans fr the manufacture f the prduct. Fllwing steps are typical: A careful review f the prduct design and specificatins t make sure that ecnmical manufacture is feasible

2 Determinatin f the methds f manufacture that will result in the manufacturing cst Selectin r develpment r prcurement f all machines, tls and ther equipment required fr the manufacture f the prduct as per the required quality and rate f prductin Layut f the prductin area and auxiliary spaces and installatin f the manufacturing facilities Planning fr and establishing the necessary cntrl f materials, machines and human resurces t ensure effective utilizatin f the manufacturing facility fr the ecnmical prductin f the prduct Basic Factrs affecting Prcess Design: Vlume r quantity f prduct t be manufactured based n sales frecast The required quality f the prduct The equipment that is available r that can be prcured fr the prduct manufacture Vlume: The vlume (quantity) t be manufactured must always be cnsidered as the vlume t be prduced within a given perid. Anticipated vlume shuld be based n Sales frecasts Greater vlume prduced the greater pprtunity t incrprate advanced methds f manufacture int the design f the manufacturing prcess. Number f identical units t be prduced vitally affects the selectin f manufacturing methds Leads t new equipment, ex. Jigs, fixtures, r dies Will lead t increased prductin capacity Prduct explsin and standardizatin: Assembled prducts are brken dwn int assemblies, subassemblies, and cmpnent parts. Mre than ne prduct invlved leads t standardizatin f subassemblies and cmpnent parts Standardizatin f cmpnent parts and prduct explsin are f primary imprtance t prcess engineering Quality f the prduct: Quality requirements affect design f manufacturing prcess. Higher quality requirements = higher manufacturing csts Prcess engineering uses the fllwing dcuments t stipulate quality. Bills f materials Parts lists Assembly and detail drawings Engineering releases

3 Equipment: The number f machines f a given type r size influence the design f the prcess Types f manufacturing: This is decided based upn the fllwing: vlume, quality, and equipment. This may be cntinuus r intermittent r mixed type. Cntinuus manufacturing is the prductin f gds n a flw basis at a predetermined rate. Flw methd requires prducts t mve cnsistently Apprach cntinuus mvement Mve frm peratin t peratin withut cntrlled strage Typically fund in fd-prcessing plants and chemical industries Line balancing must be used when planning the design f a cntinuus prcess line. Line balancing ensures that each peratin in cntinuus manufacturing requires the same amunt f time. Grup technlgy is an apprach t manufacturing in which similar parts are identified and then gruped tgether t take advantage f their similarities. Similar parts are gruped int part families Part families are manufactured in cells Manufacturing cells are made up f machine tl grupings Intermittent manufacture is ften referred t as jb-lt prductin. Usually ne r mre lts ahead f each wrkstatin awaiting prcessing Requires larger inventry f gds in prcess than cntinuus manufacturing Mixed types f manufacturing: Industries ften use cncepts such as just-in-time t integrate cntinuus and intermittent manufacturing CAD CAM: The term CAD/CAM is a shrt frm f Cmputer-Aided Design (CAD) and Cmputer-Aided Manufacturing (CAM). The term CAD/NC (Numerical Cntrl) is equivalent in sme industries. CAD/CAM sftware uses CAD drawing tls t describe gemetries used by the CAM prtin f the prgram t define a tl path that will direct the mtin f a machine tl t machine the exact shape that was drawn. Well befre the develpment f Cmputer-aided design, the manufacturing wrld adpted tls cntrlled by numbers and letters t fill the need fr manufacturing cmplex shapes in an accurate and repeatable manner. During the 1950's these Numerically-Cntrlled machines used the existing technlgy f paper tapes with regularly spaced hles punched in them (think f the paper rll that makes an ldfashined player pian wrk, but nly ne inch wide) t feed numbers int cntrller machines that were wired t the mtrs psitining the wrk n machine tls.

4 The electr-mechanical nature f the cntrllers allwed digital technlgies t be easily incrprated as they were develped. By the late 1960's Numerically- Cntrlled machining centers were cmmercially available, incrprating a variety f machining prcesses and autmatic tl changing. Such tls were capable f ding wrk n multiple surfaces f a wrkpiece, mving the wrkpiece t psitins prgrammed in advance and using a variety f tls - all autmatically. What is mre, the same wrk culd be dne ver and ver again with extrardinary precisin and very little additinal human input. NC tls immediately raised autmatin f manufacturing t a new level nce feedback lps were incrprated (the tl tells the cmputer where it is, while the cmputer tells it where it shuld be). What finally made NC technlgy enrmusly successful was the develpment f the universal NC prgramming language called APT (Autmatically Prgrammed Tls). Annunced at MIT in 1962, APT allwed prgrammers t develp pstprcessrs specific t each type f NC tl s that the utput frm the APT prgram culd be shared amng different parties with different manufacturing capabilities. The develpment f Cmputer-aided design had little effect n CNC initially due t the different capabilities and file frmats used by drawing and machining prgrams. Hwever, as CAD applicatins such as SlidWrks and AutCad incrprate CAM intelligence, and as CAM applicatins such as MasterCam adpt sphisticated CAD tls, bth designers and manufacturers are nw enjying an increasing variety f capable CAD/CAM sftware. Mst CAD/CAM sftware was develped fr prduct develpment and the design and manufacturing f cmpnents and mlds, but they are being used by architects with greater frequency. Tday, ver three-quarters f new machine tls incrprate CNC technlgies. These tls are used in every cnceivable manufacturing sectr, including many that affect building technlgies. CNC technlgy is related t Cmputer Integrated Manufacturing (CIM), Cmputer Aided Prcess Planning (CAPP) and ther technlgies such as Grup Technlgy (GT) and Cellular Manufacturing. Flexible Manufacturing Systems (FMS) and Just-In-Time Prductin (JIT) are made pssible by Numerically- Cntrlled Machines.

5 Prcess Design Prcedures The prduct designer and the prcess engineer wrk tgether during the design f the part t ensure that all pssible manufacturing prblems are taken int cnsideratin as the cmpnent part design id develped. Determine vlume quality and equipment available. Make the decisin t make r buy. If the part is t be made, the next step is t cnsider all the wrk that is required t cnvert the part frm a raw material state t a cmpletely machined r prcessed part. The wrk t be dne is gruped int peratins. Arrange the peratins int the prper sequence fr the mst ecnmical manufacture. Imprvement f prduct design fr manufacture: Often the prduct r cmpnent parts are designed s that ecnmical manufacture is nt pssible, s the part r cmpnent parts must be redesigned. In such situatins the prcess engineer has fur pssible slutins: The part may be purchased frm a cncern having the prper equipment. The necessary equipment may be mdified t prduce the part. Existing equipment may be mdified t prduce the part. The part may be redesigned s that it can be prduced n available equipment. Mst situatins the last slutin is mst feasible. All changes t prduct design and specificatins must riginate frm the prduct-engineering grup t ensure that n change made will materially affect the functinal requirements f the prduct.