Process design refers to the general term of process procedure design and process equipment design.The core of productive construction project design.It is determined according to the characteristics, nature and function of industrial production.The production process of each department is different. On the whole, the process design of industrial construction projects mainly includes the following contents: (1) Determine the production program of the workshop, explain the product specifications and output, and determine the supply conditions of raw materials, fuel, water, electricity, labor, etc.(2) Prepare the production process of the workshop, describe the production process flow, specifications and quantity of main production equipment and auxiliary equipment, determine the workshop area, plane layout and profile height of equipment, determine the demand and supply methods of power, steam, air, electricity, etc., and prepare safety technology and labor protection measures.(3) Calculate the demand for raw materials and semi-finished products of the factory, as well as the demand for transportation, communication, lighting, heating, water supply and drainage, determine the necessary man hours and labor consumption, and calculate the fixed assets, working capital, product costs and investment benefits.(4) Determine the production and operation management system of the whole plant, clarify the production tasks of each workshop and the collaboration between them, prepare the production and operation plan, product quality inspection, product supply and marketing order and other systems, and formulate the labor and production organization and work system.[1]
draw upRoutingIt's designProcess procedureThe most critical step is to complete the following work in sequence.
1. SelectPositioning datumFine datumSelection principle ofPrinciple of datum coincidenceThe design datum of the machined surface shall be selected as the precision datum as far as possible, so as to avoidpositioning error。The principle of unified datum shall select as many machining surfaces as possible on the workpiece with the same set of precision datum to ensure the relative position relationship between the machining surfaces.For example, machiningShaft partsGenerally, the two center holes are used as the unified precision datum to process all the cylindrical surfaces andend face, so as to ensure thatCoaxialityAnd end face to axis lineverticality。Principle of mutual reference When the position accuracy between two machined surfaces on the workpiece is required to be relatively high, the method of repeated machining with two machined surfaces as the reference can be used.For example,Lathe spindleFront and rear supportJournalThere is a strict coaxiality requirement between the taper hole and the spindleSpindle taper holeGrind the front and rear bearing journal surfaces of the main shaft for reference, and then grind the taper hole of the main shaft for reference on the front and rear bearing journal surfaces, and finally meet the coaxiality requirements specified on the drawing.The finishing process of some surfaces based on the principle of self reference, requirementsMachining allowanceSmall and uniform, often based on the machined surface itself, the figure is shown inslideway grinderThe surface of the upper grinder body guide rail, the machined bed 1 passesWedge iron2 Supported on the workbench, longitudinalMobile workbenchWhen pressing gently on the surface of the processed guide railDial indicatorThe pointer gives the relative position of the machined guide rail surfaceMachine tool guideAccording to this reading, the operator adjusts the four wedges at the bottom of workpiece 1 until the dial indicator pointer basically stops when the workbench drives the workpiece to move longitudinally, and then clamps workpiece 1 on the workbenchgrinding。Coarse datumThe principle of ensuring that the machined surface of the part has a certain position accuracy relative to the non machined surface. If there is a non machined surface on the machined part, the non machined surface should be selected as the rough benchmark. This can ensure that the non machined surface has a relatively accurate relative position relative to the machined surface. The surface is a non machined surfaceBoringThe wall thickness of the rear part shall be uniform, and the surface shall be selected as the rough benchmark boring, excircle turning and end turning.When there are several unmachined surfaces on the part, the unmachined surface with higher relative position accuracy requirements shall be selected as the rough datum.Reasonable distributionMachining allowanceThe principle is to ensure that the machining allowance of important surfaces is uniformCoarse datum。The guide rail surface is the most important surface in the lathe body parts. It requires not only high precision, but also uniform metallographic structure and highAbrasion resistance。When casting the bed, the guide rail surface is inverted at the bottom of the sandboxcasting molding The material of the guide rail surface is dense, and there are relatively few sand holes and air holes. Therefore, when machining the bed, the actual removal amount of the guide rail surface should be as small and even as possible. Therefore, the guide rail surface should be selected as the rough benchmark to process the bed bottom surface, and then the processed bed bottom surfaceFine datumMachining the guide rail surface, which is now removed from the guide rail surfaceMachining allowanceIt can be small and even.It is convenient to select rough datum for machining bedClampingIn order to make the workpiece positioning stable and clamping reliable, it is required that the selected rough datum should be as flat and smooth as possible, and no forging is allowedFlashCasting gate and riser nicks or other defects with sufficient bearing area.Coarse datumGenerally, the principle of not reusing is that the rough datum is generally allowed to be used only once in the same dimension direction, because the rough datum is generally rough, and between two groups of surfaces processed by reusing the same rough datumposition error It will be quite large, therefore, the coarse base shall not be reused generally.[2]
2. Selection of surface processing method
When selecting the processing method, first select itsFinal processMethods, and then select the processing methods of the relevant leading processes of the surface one by one.The same surface can be processed by different processing methods, but the processing quality, processing time and cost of each processing method are different. The task of engineering and technical personnel is to follow the specific processing conditions（Production type, equipment condition, technical level of workers, etc.) to select the most appropriate processing methods to process machine parts that meet the requirements of the drawings.Generally, the machined surface with certain technical requirements can not meet the requirements of the drawing only through one processing. For the main surface of precision parts, the processing quality requirements can be gradually met through multiple processing.For example, machining aAccuracy classITSurface roughnessFor the steel cylindrical surface with Ra of 0.2 μ m, the final process is fine grinding, and the leading process can be rough turning, semi fine turning and rough grinding respectively.After the processing scheme and process of the main surface are selected, the processing scheme and process of the secondary surface are selected.[2]
3. Division of processing stages
The main purposes of dividing the processing process of parts into processing stages in rough machining stage are: (1) to ensure the processing quality of parts;(2) It is conducive to early detection of blank defects and timely treatment;(3) It is conducive to the rational use of machine tools and equipment.In addition, dividing the workpiece processing into several stages is also conducive to protecting the finished surface from collision damage.Semi finishing stage Finishing stageFinishingConcentration and dispersion of stage processesCentralized operationIn principle, the process shall be organized according to the principle of process centralization, which means that each process shall include as many processing contents as possible, and many processes shall form a centralized process. The maximum process centralization means that all surfaces of the workpiece can be processed in one process.Traditional assembly line and automatic line production are basically based onProcess dispersionThe technological process is organized in principle, which can achieve high productivity production, but has poor adaptability to product modification and is difficult to change production.The principle of process decentralization organizes the process according to the principle of process decentralization, which is to minimize the processing content of each process. The maximum process decentralization means that each process only includes one simple processStep。Adoptionnumerical control machine、machining center The technological process is organized according to the principle of process centralization, and the production adaptability is better. It is relatively easy to change production. Although the one-time investment of equipment is high, due to the sufficient flexibility, more and more attention is still paid to it.Arrangement of process sequence Arrangement of machining process First processingPositioning datumSurface, and then other surfaces. First machine the main surface, then machine the secondary surface. First arrange the rough machining process, then arrange the finishing process. First machine the plane, then machine the hole. The heat treatment process and surface treatment process are arranged to improve the cutting performance of workpiece materials. For example, annealingnormalizing、Quenching and temperingEtc. shall be carried out before cutting.To eliminate the workpieceinternal stressScheduled heat treatment process, such as,Artificial aging, annealing, etc., arranged after the rough machining stage.In order to reduce the transportation workloadMachining accuracyWorkpieces with low requirements can also be arranged before rough machining.aboutMachine bed, columns and other complicated structurescasting, before and after rough machiningAging treatment(Artificial aging orNatural prescription）So that the material structure is stable and there is no greater deformation in the future.To improve the workpiece surfaceAbrasion resistanceHeat treatment process arranged for corrosion resistance and heat treatment process arranged for decoration, such asChrome platingGalvanizing, blueing, etc. are generally arranged at the last stage of the process.Other processes are arranged to ensure partsManufacturing qualityTo prevent waste products, inspection procedures should be arranged on the following occasions: 1) After all rough machining is completed;2) Before and after being sent to the workshop for processing;3) Long working hours and before and after important processes;4) After final machining.In addition to geometric dimension inspection procedures, some parts also need inspection procedures such as flaw detection, sealing, weighing and balancing.Burrs on the surface or inner cavity of parts have a great impact on the quality of machine assembly. After cuttingDeburringProcess.Before parts are assembled, cleaning procedures should generally be arranged.The inner hole of the workpiece and the inner cavity of the box are easy to retain chips, grindhoningetc.FinishingAfter the process, small abrasive particles are easy to attach to the surface of the workpiece, so pay attention to cleaning.In usemagnetic forceAfter the process of clamping the workpiece, arrangeDemagnetizationProcess, not allowed to haveremanenceThe workpiece of is put into the assembly line.[2]
4. Selection of machine tool equipment and process equipment
The size of the selected machine tool equipment shall be consistent with the physical size of the workpiece,Accuracy classIt shall be compatible with the processing requirements of this process, the motor power shall be compatible with the power required for processing of this process, and the automation degree and production efficiency of machine tools and equipment shall be consistent with the workpieceProduction typeAdaptation.The selection of process equipment will directly affect theMachining accuracy, production efficiency and manufacturing cost should be properly selected according to different situations.Under the condition of medium and small batch production, the selection should be considered firstGeneral process equipment(including fixtures, cutters, measuring tools and auxiliary tools);In large quantitiesMass productionSpecial process equipment can be designed and manufactured according to processing requirements.The selection of machine tool equipment and process equipment should not only consider the current benefits of equipment investment, but also consider the possibility of product transformation and production change, so that it should be flexible enough.[2]
Determination of dimensions and their tolerances
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Parts drawingThe dimensional tolerance marked on is the final dimensional requirement of the part processing. The dimensional tolerance of many intermediate processes in the process must be determined in the process of design.Process dimensions and tolerances are generally calculatedProcess dimension chainYes, in order to master the calculation law of process dimension chain, here we first introduceDimension chainThe concept of dimension chain and the calculation method of dimension chain are discussed.[2]
（1） Dimension chain and its calculation formula
1. Definition of dimension chain
In the process of workpiece processing and machine assembly, closed dimension groups formed by interconnected dimensions are called dimension chains.If the workpiece is first positioned to process surface C with surface A, the dimension A1 is obtained, and then the step surface B is processed with the adjustment method with surface A positioning, the dimension A2 is obtained. It is required to ensure the dimension A0 between surface B and surface C;A1, A2 and A0 form a closed dimension groupDimension chain。Each dimension that constitutes the dimension chain is called the ring of the dimension chain.The dimension obtained indirectly in the dimension chain is calledClosing ringIn the dimension chain shown in Figure b, A0 is the indirectly obtained dimension, which is the closed ring of the dimension chain shown in Figure b.All dimensions in the dimension chain directly obtained through processing are called composition rings. A1 and A2 in the dimension chain are dimensions directly obtained through processing, and A1 and A2 are composition rings of the dimension chain.The composition ring can be divided intoIncreasing ringAnd minus ring.When the size of other composition rings remains the same, if the closed ring increases with the increase of a composition ring, this composition ring is called an increasing ring;If the closed ring decreases with the increase of a composition ring, the composition ring is called a minus ring;In the dimension chain shown in Figure b, A1 is the increase ring and A2 is the decrease ring.[2]
According to the position relationship of dimension chain in space distribution, it can be divided into linear dimension chain, plane dimension chain and spatial dimension chain.[2]
3. Calculation of dimension chain
There are three types of dimension chain calculation: forward calculation, inverse calculation and intermediate calculation.Find the known composition ringClosing ringIs called positive calculation;It is called inverse calculation to find each component ring with known closed ring;Given the closed ring and part of the constituent ring, finding the remaining one or several constituent rings is called intermediate calculation.Dimension chain calculation YesExtremum methodAnd statistical methods.Solving dimension chain with extreme value method is to solve the problem from the extreme value condition of each link in the dimension chainclosed loopRelating to the size of the component ring.Using statistical method to solve the size chain is to use the theory of probability to find the relationship between the size of the unsealed closed loop and the size of the composition loop.[2]
（1）Closing ringThe basic dimension Ao is equal to allIncreasing ringThe sum of the basic dimensions (Ap) minus the sum of the basic dimensions (Aq) of all rings, in which: m - the number of rings;K-increasing ring number;ξ i - size transfer coefficient of the ith composition ring. For linear size chain, ξ i=1 for increasing ring and ξ i=- 1 for decreasing ring.(2) ToroidalUltimate dimensionAmax=A+ESAmin=A-EI (3) ringLimit deviationES=Amax－AEI=A－AminBasic dimensionsLimit deviation, tolerance and intermediate deviation (4)Closing ringIn the middle deviation formula of, Δ i - the middle deviation of the ith composition ring.(5) Closed ring tolerance (6) Middle deviation of composition ring Δ i=(ESi+EIi)/2 (7) Limit dimension of closed ring (8) Closed ringLimit deviation。[2]
5. Solving straight lines by statistical methodDimension chainBasic calculation formula
The size distribution in mechanical manufacturing is mostlyNormal distribution, but there areNon normal distributionThe non normal distribution has symmetric distribution and asymmetric distribution.In addition to some basic formulas for solving linear dimension chain by limit method, there are two basic calculation formulas for solving dimension chain by statistical method: (1)Closing ringIntermediate deviation (2) In the closed ring tolerance formula: ei - the asymmetry coefficient of the size distribution curve of the ith composition ring;EiTi/2 - dimension of the ith composition ringDistribution centerbe relative toTolerance zoneOfOffset；Ko - relative distribution coefficient of closed ring;Ki - the relativity of the i-th constituent ringDistribution coefficient。E and k values of different distribution curves[2]
Dimension chain analysis
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1. Calculation of process dimension tolerance when the positioning datum does not coincide with the design 2. Calculation of process dimension and its tolerance when one processing meets multiple design dimension requirements 3. UseProcess sizeCalculation of process size and allowance by chart tracing method[2]
When sky.net formulates the process or analyzes the current process, it often encounters the process size conversion due to the non coincidence of the existing benchmarks, andProcess benchmarkThe multiple conversions of, as well as the influence of process margin changes, there are more complex datum relations and dimensional relations in the whole process.In order to complete the processing process of parts economically and reasonably, a set of correct and reasonable process dimensions must be formulated.In this case, the above individual can be appliedDimension chainTo solve one by one, it can also be comprehensively calculated by chart tracing method or tolerance table method.[2]
The technological process related to the axial surface of a sleeve type part is as follows: process 1. locate the large end face A, turn the small end face D, and ensure the overall process size A1 ± T (A1)/2;When the car is small, the outer circle reaches B, and M is guaranteed.Process 2. Position the small end surface D, finish turning the large end surface A, and ensure that the overall process size is A2 ± T (A2)/2;Bore large holes to ensure that the hole depth to surface C is A3 ± T (A3)/2.Procedure 3. Position the small end surface D, grind the large end surface A, and ensure that the overall size A4=L.[2]
