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Unit 13 Automated Production Lines Unit Introduction Unit Learning Objectives Fundamentals of Automated Production Lines Applications of Automated Production Lines Analysis of Transfer Lines
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13.1 Introduction Automated production lines. Các dây chuyền sản xuất tự động bao gồm các vị trí làm việc được kết nối với nhau bằng các hệ thống di chuyển nhằm mục đích di chuyển các chi tiết từ vị trí làm việc này đến vị trí làm việc khác. Automated production lines are usually expensive to implement. Việc xây dựng các dây chuyền khá tốn kém, ví dụ như dây chuyền tự động hóa cứng, layout của chúng hầu như không thể thay đổi một khi được xây dựng và lắp đặt trong nhà máy. các điều kiện sau đây phù hợp với việc sử dụng dây chuyền tự động:
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13.1 Introduction 1. High product demand, requiring high production quantities 2. Stable product design, as automated production lines cannot accommodate frequent design changes 3. Long product life—typically several years 4. Multiple operations, involving the use of a number of workstations
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13.1 Introduction Khi các điều kiện được thỏa mãn, các lợi ích có thể dễ dàng nhận ra khi sử dụng các dây chuyền tự động: 1. Low amount of direct labour 2. Low product cost 3. High production rate 4. Minimal work-in-progress and production lead time 5. Minimal use of factory floor space
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13.3 Fundamentals of Automated Production Lines In automated production un-processed parts enter the production line and undergo a system of automated processing at various workstations along the fixed production line, with parts being moved from one workstation to the next by means of a mechanized work transport system, until the last process occurs to the part at the final workstation in the system, at which point the part exits the automated production line. The automated production may consist of, besides automated workstations, manual workstations and inspection stations.
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13.3.2 Workpart Transfer Mechanisms The function of the workpart transfer system is to move parts between stations on the production line, a function performed by means of transfer mechanisms that are either synchronous or asynchronous. Synchronous transfer is the traditional method of moving parts within a production system, but asynchronous transfer has the following advantages: Greater flexibility Fewer pallet fixtures needed Easy to rearrange or expand the production system
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13.3.2.1 Linear Transfer Systems Types of linear transfer systems used for workpart transfer include powered roller conveyors, belt conveyors, chain driven conveyors, and cart-on-track conveyors previously described in unit 8. The typical installation of a conveyor system for workpart transfer is depicted in Figure 13.3 Cart-on-track conveyors provide asynchronous movement of parts, and are designed to position their carts within about ±0.12mm, which is adequate for many processing operations
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13.3.2.1 Linear Transfer Systems Linear transfer lines also come in the form of walking beam transfer systems, where parts are moved synchronously by means of a transfer beam that lifts parts from their respective stations and transfers them one position ahead.
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13.3.2.2 Rotary Indexing Mechanisms Several mechanisms can be used to generate the type of rotary power required by rotary indexing machines. Two of these are the Geneva mechanism, and the cam drive.
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13.3.2.2 Rotary Indexing Mechanisms In general: degrees of rotation ns is the number of slots in the Geneva dwell time is given by: Geneva mechanisms with four, five, six, or eight slots are common. we can determine total cycle time as:
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EXAMPLE 13.1 A rotary indexing table is driven by a five-slotted Geneva mechanism. The driver rotation is 50 revolutions per minute. Determine: 1. The total cycle time of the indexing table 2. The available processing time for the indexing table 3. The time lost each cycle to index the table (repositioning time)
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13.3.2.2 Rotary Indexing Mechanisms Cam drive mechanisms may also be favoured as an alternative to the Geneva mechanism (see Figure 13.7).
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13.3.3 Storage Buffers Automated production lines may also contain storage buffers, which act as temporary storage for parts that are traversing the line, before being released from the buffer so that they may proceed to downstream workstations. Storage buffers may be deployed on automated production lines in manual or automated arrangements. Automated versions consist of mechanisms for capturing and releasing parts to the production line, and a structure storage buffer for holding the parts.
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13.3.4 Control of the Production Line 13.3.4.2 Line Controllers Programmable logic controllers are used for automated production line control. Other control systems may be developed using PCs supplied with control software, and designed for the factory environment. Computer control has the following advantages: Computer control can be upgraded, to keep in step with developments of the automated production line. Computer control can record operational data for subsequent analysis, or for legal reasons. Computer control can create diagnostic routines to expedite maintenance and repair when line breakdowns occur. Computer control can generate preventative maintenance schedules. Computer control offers a more convenient human-machine interface between the operator and the automated line.
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13.4 Applications of Automated Production Lines Automated production lines are found in both processing and assembly environments, but here we focus upon processing applications, in particular operations of machining. Other processes that can be performed include sheet- metal forming and cutting, rolling mill operations, spot welding, painting, and plating operations.
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