Design of process of cylinder head assembly and fabrication

Contents

CONTENTS

Section 1. Development of process diagram of assembly unit assembly

1.1. Purpose of the node. Identification of main technological tasks                   

1.2. Constructability Analysis                                        

1.3. Calculation of the dimension chain by two methods  6                                      

1.4. Development and justification of the process diagram of the general assembly                 

1.5. Development and justification of process diagrams and sketches of the assembly         

1.6. Development of assembly process with equipment selection, 

tools, technical normalization of time and determination of total 

assembly labor intensity of the assembly                                                      

Section 2. Part Manufacturing Process Route Design

2.1. Assigns a part to a subassembly. Part Drawing Specification Analysis        

2.2. Workaround of part design for processability                            

2.3. Part Material Justification: Operating Condition Selection Criteria, Material Options  

2.4. Selection and justification of procurement method 18                               

2.5. Machining routes of the main surfaces of the part, their justification   19         

2.6. Development of a common manufacturing route                  

2.7. Development of process adjustments for 1st - 2nd operations with selection of cutting tools, justification and calculation of processing modes     

List of literature 26                                        

Development of process of assembly assembly       

  1.1   Purpose of the article. Analysis of technical requirements for assembly, identification of the main technological tasks: development of control diagrams for the main parameters.

      The assembly unit "Cylinder Head" is an integral part of a single-cylinder diesel engine and is designed to control the gas distribution phases by means of inlet and outlet valves, as well as to ensure the tightness of the cylinder. The product is a head body (pos. 1) made of aluminium alloy with valve seats pressed into it (12, 13 ) and guide bushings (11, 14). Valves (inlet (position 2) and outlet (position 3) can move freely along guide bushings. Springs (pos. 7) elastically support the valves, ensuring their self-return. The head body has inlet and outlet channels, which are holes with a curvilinear axis, through which the mixture and exhaust gases from it respectively enter the combustion chamber. At the points of contact of bushings and head housing there are oil reflecting caps preventing oil ingress into the cylinder. Studs are also wrapped in the head body to attach supply and discharge devices.

With the help of a gas distribution mechanism (in particular, a camshaft), valves are alternately lowered along the bushings. Note here that cylinder is filled with mix and exhaust of gases therefrom. Springs provide self-return of valves to initial position.

    Operating conditions:

- temperature 800900 (supported by cooling system)

- pressure in inlet channel: 0.4 MPa; in the outlet: atmospheric

- Load characteristics: dynamic, alternating loads due to the operation of the crank mechanism, as well as impacts of the valves themselves.

-Unaggressive medium: diesel fuel particles suspended in purified air (particle size 0.0020.005mm) 

Based on the operating conditions, the following technical requirements are imposed on the assembly structure:

Rub the butt of the valves with the saddles until a continuous belt is at least 1 mm wide. The requirement is assigned to ensure the tightness of the valve-seat joint. If this requirement is not met, there will be untimely penetration of the mixture into the combustion chamber, as well as untimely release of gases from it, which will lead to a violation of the gas distribution phases. The requirement is controlled by pouring kerosene into the channels and checking (visual) its penetration through the valve-seat joint. The requirement is provided by fitting of the joint using abrasive material (abrasive paste based on: micropore 25A  M7N GOST 2881890 and motor oil M8V GOST 1054178) 

2 Recessed valves relative to surface A 1.0-1.5 mm. It is designed to ensure safe operation of valves in a strictly defined range, in case of violation of the limits of which there may be collisions of valves with the piston and failure of the gas distribution mechanism. Failure of valves is possible. This requirement is controlled on the device shown in the control diagram. The requirement is ensured by the execution of assembly parts within the specified tolerances, as well as by racing work. 

Perform flapping of valves before installation of oil reflective caps. The requirement is intended to facilitate valve lapping and to keep the caps in good condition. In case of non-fulfillment, the caps will interfere with their rubber seals freely moving the valves along the bushings, and abrasion and failure of the seals themselves will occur. Visual control is provided by the collector.

Leak check of valve joints, pos. 2 and 3 with a pneumatic device with a pressure of 0.59 MPa + 20%. Air pressure shall be supplied from surface A. Air leaks shall not be allowed .             The requirement is assigned to ensure the tightness of the valve-seat joint and regulates the value of air pressure during the check and the direction of its supply. If not performed , the tightness can be checked incorrectly: the pressure may be excessive or insufficient. The requirement is controlled by the instrument (pressure gauge) located on the bench. The requirement is provided on the bench (test bench ST453), which is a compressor unit with the ability to attach the product to it and ensure tight contact between the head and the supply system.

The main technological tasks that arise during the assembly of the head are: 1. Ensuring the exact adjoining of the valves to the seats along the entire surface of the joint .

Tightness of joint

 2.1 Analysis of constructability of assembly unit

The assembly unit "Cylinder Head" is a set of parts and assemblies assembled mechanically into a full-fledged, structurally completed product, the assembly of which does not require high qualification of the worker and does not involve complex equipment . The design of the article provides for a minimum number of parts and components, at which its operability is ensured: in the article there are 15 parts and one assembly unit - oil reflective cap (1 SB20). Convenience of assembly is provided: mainly connections with guaranteed clearance (bushing valve), there are connections with interference (head seat, head bushing), there are no non-detachable connections, there are connections with elastic elements - springs, threaded connections (studs pos.15). Racing work has also been reduced to a minimum (these include valve-to-saddle actions). This racing work is carried out on simple, affordable equipment . It is well ensured that parts having quick-wear surfaces can be replaced (during operation, wear is possible on the rubbing surfaces of the valves: along the valve rod, and the valve plate is worn out; therefore, it is possible to press out old bushings and saddles and press new ones into these places, as well as replace the valve itself).  The principle of unification is not fully respected: the inlet and outlet valves have different tray diameters, as a result of this, the seats also have different diameters. Of the standard parts in the assembly, only studs and springs. All parts and assemblies are interchangeable, in case of failure, spare parts are installed in their places. The possibility of mechanization and automation of assembly works is not provided: assembly is carried out in compliance with completeness, release of valves and head after lapping is not allowed. Convenient access to places of control is provided. Control is carried out by simple design and accessible means (gauges, indicators, visual inspection), for example, drowning of valves can be controlled by a caliber, a uniform belt on the surface of the valve after lapping can be controlled by universal measuring means. The free approach of the components of the assembly equipment is provided (the punch of the press does not hit the protruding parts of the product design , the head of the cap can move freely). In order to improve the accuracy of the installation, special elements are provided in the design that are assembly bases (for example, the surface of the villages 12, 13 is the base for valves). Combined design, assembly, installation and measurement bases: surface A (see drawing) is assembly, installation and measuring. On the basis of the above, the design of this product can be considered technological for serial production conditions.

1.5. Development and justification of process diagrams and sketches of the assembly

The considered knot represents "A maslootrazhatelny cap" (1SB20) which protects internal space of a head of a cylinder from oil penetration. This knot gathers separately from the product "Cylinder Head" (SB1). Its components are a metal body - a basic part (pos.20 ) and a rubber cuff (pos.2). During assembly of this unit, the cuff is installed on the housing by interference fit. The presence of this node reduces the labor consumption of the general assembly, because it is assembled in parallel with it.

1.6. Development of assembly process with equipment selection, 

tools, technical normalization of time and determination of total 

labour intensity of  assembly of the assembly.

     On the basis of the developed process diagram , the assembly process was compiled. Based on the principle of homogeneity and completeness of actions at one workplace, operations were identified. The installation and fixing scheme of the base part has been determined, equipment (pneumatic press, hairpin, etc.) has been selected. Further, the calculation of pressing forces was made, as well as operating times are calculated according to normative data.  

    Sketches are shown on sheet 1. A detailed description of the assembly process route is provided in the roadmap.

Calculation of pressing forces during pressing of bushings (pos.11.14) and valve seats (pos.12.13) in operations 015 and 020.

Section 2 Design of the part manufacturing process route.

  2.1 Part assignment in the unit. Analysis of the technical requirements of the part drawing, identification of the main technological tasks, development of control diagrams for the main accuracy parameters.

    The part is a body cast from aluminum alloy AK9M2KT6 GOST 158393, in the design of which cooling ribs , inlet and outlet channels, as well as seats for pressing the seats and guide bushings of valves are provided.  This Cylinder Head part is the body part for the Cylinder Head assembly. Inlet and outlet channels direct flows of combustible mixture into cylinder, and exhaust gases are directed and withdrawn from cylinder.  

Technical Requirements Analysis: 

   1. Check of perpendicular axes of all threaded holes, except for specified ones, relative to surfaces on which they are located, 0.2 mm on the length of 100mm. 

Assigned to ensure that the axes of the threaded holes are positioned accurately within the specified boundaries. Failure to do so may cause difficulties in securing the article structural elements in these threaded holes. It is controlled by a special device . The requirement is provided by the machine on which the processing will be carried out, as well as the rigidity of the technological system.

  2. Roughness of casting surfaces Rz320. Assigned to provide surface roughness of a given value. In case of non-performance, harmful swirls may occur in the inlet and outlet channels, which will lead to incorrect operation of the head. It is controlled by a profilometer or roughness samples. It is provided by the casting method, which produced the blank.

    3. Check inlet and outlet channels for tightness with pressure 0.1 MPa during 1 min in water bath with pressure 0.1 MPa. Air bubbles through the thickness and casting walls are not allowed . It is assigned to ensure tightness. If the requirement is not met, the operating engine may have a leaking cylinder head, at the same time it will not perform its functions. Controlled at the stand. It is provided at the stage of procurement production during production of a blank. The following is a control diagram.

4. Deviation from perpendicular of axis of ∅13N8 and base surface A not more than 0.05 mm by 100 mm of length.

This requirement is assigned to ensure that the sleeve fit hole and the base plane are perpendicular. If this requirement is not met, the valve will skew during operation, which may cause severe wear of the valve and its bushing. This may result in a malfunction of the head. The requirement is provided by the drilling machine on which the processing will be carried out.

5. The parallelism of the lower sealing plane of the head with respect to the base plane A is 0.03 mm on a length of 100 mm. The requirement is assigned to ensure that the specified surfaces are parallel. If the requirement is not met, the subsequent processing of the part may be difficult, namely, when milling the holes for the seats of the valves, the milling mill will skew. It is controlled by the accessory, then the test diagram is presented. Provided by milling.

  Based on the analysis of technical requirements, the following technological tasks can be distinguished: 1. Monitoring of leak tightness of inlet and outlet channels. 2. Provision of preset roughness and cleanliness of casting surface inside channels. 

3. Maintaining deviations of mutual arrangement of surfaces within the specified limits.

2.2 Workmanship of the part design for the specified type of production

1. The part has a complex configuration, combining a large number of shaped surfaces (cooling ribs, surfaces of the inlet and outlet channels). The design of the part is as simple as possible, but at the same time provides a large amount of machining. The part has reliable base surfaces.

To comply with the principle of constancy of bases, as well as for the convenience of basing, artificial bases are used in processing.

2. Practically all the accuracy requirements specified by the designer are justified and correspond to the operating conditions, there are no overestimated requirements:

 8th quota , roughness parameter is not higher than Ra0.63.

3. The design of the part complies with the principles of standardization and unification. Dimensional unification: most dimensions from the normal series; element unification: chamfers  ,

grooves. This allows you to use standard tools and equipment in processing.  

4. The part has significant rigidity (it has an almost cubic shape), and the dimensional ratios of the part imply the use of a rigid tool and high-performance processing methods..

5. Ease of tool feed during machining is ensured: machined surfaces are located outside, there are no hidden and difficult to process surfaces. There is also provision for through processing of holes (holes for fitting of valve bushings).

6. Specific requirements for the part are met using high-performance methods (use of CNC): processing is carried out with a minimum number of installations on the machine, hole diameters are typed as much as possible, symmetrical sections are not made the same in shape and size, which will not allow processing on the CNC machine by changing only the sign. It is not possible to correct the latter drawback due to the structural differences between the inlet and outlet channels. 

7. Parallel machining is possible (for example, side surfaces of the head can be milled parallel to a set of cutters on a horizontal milling machine).

Based on the above, the design of the part can be considered technological for a serial type of production.

2.3. Justification of part material selection: selection criteria, operating conditions, possible material variants.

    The cylinder head part is part of a single-cylinder diesel internal combustion engine, the performance of which implies its extremely low mass, i.e. the material of the part must have low density and at the same time strong . The material must have good thermal conductivity to effectively remove heat from the heated cylinder. Also important for the part material is the corrosion resistance property for atmospheric failure , in which it does not interact with ambient air. An important role is played by the cost of the part material in the conditions of mass production and its availability on the market. 

     Operating conditions are a complex loaded state. These include a set of alternating (forces of different directions in the intake, exhaust cycles), impact loads (impacts during ignition of the mixture in the cylinder and operation of the crank gear), as well as pressure forces in the inlet channel. The temperature mode  of 80900C is supported by the cooling system.

   Based on the purpose  and analysis of the operating conditions of the product , the following criteria for choosing the material of the part can be distinguished: the material must be light, strong, have good thermal conductivity, corrosion-resistant and cheap. Such materials may be aluminum alloys. 

Alloys with a high Zn content (above 3%) of AlSiZn (AL11) and AlZnMgCu (AL24) systems have increased density and reduced corrosion resistance, but have good casting properties and can be used without heat treatment. Alloys with a high content of C (over 4%) - double alloys of AlSi (AL7) and alloys of the triple system of AlCuMn with the addition of Ti (AL19) in terms of heat resistance surpass the alloys of the first three groups, but have slightly reduced corrosion resistance, casting properties and tightness.

Alloys of the system AlCuMgNi and AlCuMgMnNi (AL1, AL21) are characterized by high heat resistance, but are poorly treated.

The properties of casting alloys vary significantly depending on the casting method; they are higher, the faster the crystallization rate and the feeding of the crystallizing layer. As a rule, the highest performance is achieved with chill casting. The properties of the separately cast samples may be 2540% superior to those of the crystallized most slowly or poorly fed parts of the casting. Some alloying elements for some alloys have a detrimental effect on others. Silicon reduces the strength of alloys of AlMg systems and degrades the mechanical properties of alloys of AlSi and AlCu systems. Tin and lead, even in tenths of a percent, significantly lower the melting point of the alloys. The iron content is controlled depending on the casting method: it is maximized when casting under pressure and into a chill and is greatly reduced when casting into the ground. By reducing harmful metal and non-metal impurities in alloys using pure charge and refining, by introducing small additives Ti, Zr, Be, modifying alloys and their thermal treatment, the properties of shaped castings from A.S. can be significantly improved. Refining is carried out by blowing with gas (chlorine, nitrogen, argon); exposure to fluxes containing chloride and fluoride salts; by vacuum aging or a combination of  these methods.

Thus, for the manufacture of the part, it is advisable to choose the aluminum alloy AK9 (AL4), which, in its purpose and properties, satisfies the operating conditions.

 2.4 Selection and substantiation of procurement method: selection criteria, diagram.       

    Process characteristic of part material

Alloy AK9 (AL4) has good casting properties : low shrinkage porosity, high fluid flow, insignificant shrinkage. At the same time, pressure treatment of this material is practically impossible: cracking is possible, and, as a result, a significant decrease in strength.

 Part Shape 

     The "Cylinder Head" part is a body having complex internal channels, on the outer surface a plurality of ribs designed to cool the head, as well as other shaped surfaces that complicate the manufacture of the workpiece.

  Based on the complexity of the shape of the part, it is possible to manufacture a blank by casting.

Required manufacturing accuracy, surface roughness  

Most of the surface of the workpiece is machined and does not require high manufacturing accuracy, but there are non-workable structural elements of the part having roughness requirements (for example , the surfaces of the inlet and outlet channels have roughness Rz320). Precision requirements can be met by the following casting methods: sand-clay casting, injection molding.   

Production type

Production type is serial. With this type of production, it is economically more justified to cast into sandy-clay forms.

Based on the type of production of the degree of complexity of the part, the workpiece can be made by casting into sandy-clay molds with manual molding in rods .

 2.5-2.6 Route of part main surfaces processing, their justification.

  

    In the first machining operation, permanent bases are prepared for subsequent machining operations. Side and bottom surfaces of blank are taken as rough base. Then, based on them, four holes are processed, two of which are made according to IT8. These holes will then serve as the base for post-treatment (cylindrical and cut fingers)  

   Based on the design documentation, a route for processing the main surfaces of the part was developed, equipment and a tool were selected. This process is presented in the roadmap.