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  • Cylinder head machining

    Discussion in 'Machining' started by Kuba, Apr 13, 2013.

    1. Kuba

      Kuba New Member

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      Hi everyone,

      I'm a Production Engineering student and I'm working on the project concerning cylinder head manufacturing process. I would be most grateful if you could spare some time and explain me what does the process look like after casting and emptying the inner spaces of sand cores? How many times do the flat surfaces need to be milled to match required dimensions? What's there to be bored? How long do the operations last?

      I look forward to your replies.
       
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    3. bill7718

      bill7718 Member

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      As a former tool and die maker I have used most machines, both CNC and manual. To produce a variety of parts from many materials. I'll need to see what you are speaking of, If you have CAD files, I use SolidWorks, SolidEdge, Inventor, AutoCad, 3Ds Max, and Rhino. I also have Illustrator, Coreldraw,PhotoShop and Faststone Image Viewer.
       
    4. tomwuofjizu

      tomwuofjizu New Member

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      Hi, Kuba, Try to explain to you: for example of casting, when we finish pouring and it cool down, we should:
      1. cut off the runner & riser;
      2. grind off the parting lines, sands, left runner & riser etc;
      3. Sand blasting;
      4. Rough machining,
      5. final machining,

      Different parts have different requirements and processes.

      Skype: wutao5415
       
    5. Steve6br

      Steve6br Member

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      I used to work for Honda in the UK machining cylinder heads, gearbox cases and engine blocks. After casting, the cylinder heads are put through a machine to remove the "sprues" and are then heat treated. The parts are quite soft after casting. Most of the machined surfaces are processed in one pass, with the casting being passed from CNC machine to CNC machine via a "transfer line". You ask about cycle times and this is dependant on the output required from the manufacturing plant. For a higher output, the manufacturer has to install more CNC machines and performs fewer cycles with each one. Typically, the critical areas of a cylinder head are the gasket surfaces, especially the Cylinder head gasket that seals against the block, and the valve guide and seat areas. In the case of an aluminium cylinder head, the valve guides and seats need to be rough bored by a drilling style operation and then have inserts fitted that are "final machined" using a combined tool that in some cases reams the valve guide and cuts the valve seats in one operation. This ensures they are concentric and the valves seal well. The cylinder head gasket face needs to be very flat and have a defined surface finish. Too smooth and the gasket will not "key" and seal properly. Depending on the engine design, sometimes it is necessary to line bore the camshaft bearings within the head casting. If this is required, the bearing journals are cast separately and the mating surfaces of the cyl head machined including the drilling / threading of any bolt holes. The journals are then bolted on and tightened home. A long boring bar with a cutting insert for each bearing is then fed into the casting and bores each cam bearing journal in one operation. This "one operation" process saves cycle time and ensures all bearings are concentric. The camshaft seal housings are slightly less critical and are often machined separately. The process for Iron cylinder heads is not that different but I believe the castings are not heat treated and the valve seats are machined directly into the casting. Separate valve guides are still normally used to provide a better sliding surface than the cast iron. I hope this helps
       
    6. Kuba

      Kuba New Member

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      Many, many thanks for your interest and satisfying replies. I really couldn't ask for more! I appreciate your help greatly. As I have never actually seen the production line of the cylinder heads it was hard for me to imagine but now that you have explained it to me it is much clearer.
      Dear Steve6br, since you're definitely an expert on the topic, could you add a word of advice based on your experience at Honda, whether it is better to assign certain CNC machines to perform certain kind of operation or to distribute single cylinder heads to whatever machine is currently unoccupied? Perhaps it is depandant on the characteristics of the production itself and the factory's capability?
      I look forward to your support. Best regards.
       
    7. Steve6br

      Steve6br Member

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      You are welcome for the help. Regarding the CNC machine approach, I would say that the answer lays in the volumes you want to produce. If your factory was making engines for F1 you may want to use only a few machines to do all of the operations required - the fact that you may only machine one engine per day doesn't matter! If you also consider that a single CNC machine can probably only machine a maximum of 5 faces of the cylinder head without being turned over by an operator or robot etc, the jigging becomes a challenge if you try to use one machine to do all the operations. Where can you clamp the casting so that the clamps aren't also machined! For mass production, the machines are normally dedicated so that the jigs and fixtures are more simple and to minimise cycle time. In my opinion, the "cell" approach you describe as an alternative may be useful in the case of lower volume production where flexibility is key. Also consider that if every machine is capable of machining an entire engine, every machine will need to have a duplicate of every tool and fixture for every model of engine or type of component it may have to process. Economics would soon get in the way as valve seat tooling for example is very expensive. In addition, some processes such as gasket face milling need very heavy rigid machines while others such as hole drilling and tapping are best performed on a lighter, faster machine. To have all machines heavy would prove slow and expensive if you wanted to take the "flexible approach".... I hope this helps
       

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