Excellence in Manufacturing...Moving towards Moving Line Concept of Assembly

Transcription

1 Edition-5 Official magazine of L&T Plastics Machinery Limited August Excellence in Manufacturing...Moving towards Moving Line Concept of Assembly

2 Excellence in Manufacturing...Moving towards Moving Line Concept of Assembly At L&T Plastics Machinery Limited (LTPML) Excellence in manufacturing is a watchword that runs across all strata of organization and the zeal to continually maintain it is an ongoing process. One such step recently adopted by us was implementation of Moving Line concept of assembly. While this practice is very much in vogue with many of the leading automobile manufacturers where volume of production is on higher side - it is yet to catch up with machinery manufacturers. Conventional process of machine assembly confines all activities to a stationary place where the assembly starts with machine base and all other components are added on to it. Then the fully assembled machine gets painted and later tested before being shipped out of factory. It is akin to batch production concept with attendant disadvantages such as huge pile of inventory, longer lead times and uncertainty in predicting the correct readiness date of a machine. Clamp unit Injection unit Plasticizing unit Electrical cabinet Using the above sub-assemblies, final assembly used to be carried out after which testing was done. It is similar to the concept of modular assembly. Further fine tuning of the process was done by carrying out testing of each subassembly in the respective testing rigs/ powered bases before taking it up for final assembly. Even this improved method of machine assembly was not good enough as the through-put time and material handling time continued to be on higher side, also transit damages and assembly interruptions continued, though on a lower scale, all leading to uncertainty in prediction of machine readiness date. It was at this time that we wanted to graduate to the next higher level of machine assembly viz Single Piece Flow or Moving Line concept. To overcome the above mentioned drawbacks the next step we adopted was to build individual subassemblies such as: Base with piping and power pack duly mounted

3 Excellence in Manufacturing...Moving towards Essentially we have divided the entire process of machine assembly and testing into 10 distinct stages with each stage getting completed in the respective station of the moving line. Line balancing has been carefully done in such a way that each station consumes equal time matching to the takt time, thereby no station remains idle. Painted and tested sub assemblies are fed to the line and different stages of final assembly gets carried out at respective stations. Each station is self-sufficient with requisite components and subassemblies that are needed in that particular station kept at designated places. Also each station is equipped with tools & tackles which are of advanced technology, thereby easing fatigue of operators and at the same time ensuring consistent quality of workmanship. To ensure that work instructions are clear to operators, Standard Operating Procedures (SOPs) and quality checks Plasticising Unit SOPs... Moving Line Concept of Assembly that are to be performed in each station is displayed on easily readable boards with pictorial representation. The machine moves from one stage to the other on a powered platform which is mounted on rails and leveled precisely. Fully tested machine cleared at the last station is ready for shipment without further operations. The whole process is system driven with least scope for any errors and hence the quality of machine is 100% assured. We have on-line production tracking system through which position of each machine in the assembly line can be tracked and monitored. With the above manufacturing practice in place, we have considerably enhanced our machine building capacity. Also, we are now able to serve our customers better with faster deliveries. - K.R.Prashanth & V.Padmanaba Bhat Tested Injection Unit Process Capability Studies.An insight into Cpk values It is practically impossible and also economically not viable to have 100% inspection of components, produced in bulk. At the same time, any quality problem detected at customers end can result in line stoppages and the associated cost incurred could be prohibitively high. Controlling process variable to produce parts within specified limits is an approach one can implement to overcome these challenges. Establishing a process through carefully conducted process capability studies ensures that these requirements are met. A capable process is one where almost all measurements fall inside the specification limits. This can be represented pictorially by the plot below: Process capability values (Cp) represent potential of a process to consistently produce a given dimension or characteristic, but does not indicate whether the process is shifted from the mean specification. Hence a measure (Cpk) which takes care of the design specification is required to guarantee a capable process. In other words, LSL actual process spread allowable process spread USL X the factor Cp only assesses the spread of the distribution curve in relation to the tolerance band. Cpk expresses the position of the mean in relation to the tolerance. if µ and σ are the mean and standard deviation, respectively of the normal data and USL & LSL are the upper and lower specification limits, then the population capability indices are defined as follows: Cpk value together with X-R chart will represent the capability of the process to consistently produce parts within specified limits. Higher Cpk value indicates better capability of the process to meet the design specifications. Carrying out these studies by collating data manually is a tedious process and hence to address this issue LTPML injection moulding machines offer advanced package in the machine Ibed. This enables computation of Cpk values for the significant process parameters and can be carried out at pre-determined intervals based on time elapsed or no. of cycles. For a quality conscious processor, machine to compute Cpk values alone is not sufficient. What is needed along with the above feature is a machine which can consistently replicate process parmeters to achive high values of Cpk over extended period of time. LTPML range of machines score high on this point - Benny Mathew Cp = USL - LSL 6σ Cpk = min [ USL - µ, 3σ 8: 15 12: 15 16: 35 USL UCLx LCLx LSL µ - LSL 3σ Distribution Frequency Range UCLr UCLx LCLx UCLR Pp Ppk Values denoted are for illustration purpose only

4 LTPML ACE GenXt SERIES Tonnage : 60T to 1000T. Shot Weight Capacity (PS) : 21gms To 6643 gms. Screw Size (mm) : 18 to 130. Tie bar distance (mm) : 320 X 320 To 1400 X Mould Opening Stroke (mm) : 310 To Pump Unit (kw) : 11 To 110. ASWA SERIES Tonnage : 40T to 1000T. Shot Weight capacity (PS) : 21 gms To 6643 gms. Screw Size (mm) : 18 to 130. Tie bar distance (mm) : 320 X 320 To 1400 X Mould Opening Stroke (mm) : 310 To Pump Unit (kw) : 11 To 110. International Standard With CE Marking Inteligent Icon Control System With Touch Sensitive Operator Interface. Ergonomical & Modular Design To Reduce maintenance Cost Unmatched Overal Performance With Next Generation Features ENERGY SAVING SYDFEE Pump with CLOSE LOOP control of flow & pressure RUGGED & FAST, WITH EXCELLENT MOULD SAFETY FEATURE PROVEN MODEL WITH MORE THAN 2500 MACHINES RUNNING WORLD WIDE. CUSTOMISED MACHINE FOR BROAD RANGE OF APPLICATION. DE TECH SERIES Tonnage : 40T to 550T. Shot Weight Capacity (PS) : 21gms To 4108 gms. Screw Size (mm) : 18 to 110. Tie bar distance (mm) : 320 X 320 To 870 X 870. Mould Opening Stroke (mm) : 310 To 980. Pump Unit (kw) : 11 To 90. S TECH SERIES Tonnage : 60T to 275T. Shot Weight (PS) : 96 gms To 1487 gms. Screw Size (mm) : 30 to 80. Tie bar distance (mm) : 320 X 320 To 645 X 645. Mould Opening Stroke (mm) : 310 To 600. Pump Unit (kw) : 11 To 37. Clamping System Close Loop With Proportional Valve User Friendly, Swift & Transparent Control System. Robust Injection Unit With Excellent Melt Homogeneity Precise Moulding Capability With Close Tollerance On Part Dimension & Shot Weight Consistency Standardised Machine With Proven Hydraulics User Friendly Controls Low Investment & Operating Cost Best Machine For Entry Level Processors Power Saving Servo Pumps Energy Saving Upto 40%& Low Connected Load No Limitation On Hold - On Time Processing Commodity & Enginnering Plastics DTS SERIES * Tonnage : 60T to 1000T. Shot Weight (PS) : 21 gms To 6643 gms. Screw Diameter (mm) : 18 to 130. Tie bar distance (mm) : 320 X 320 To 1400 X Mould Opening Stroke (mm) : 310 To Pump Unit (kw) : 5.5 To 46. Above 550T, It is available as DTS-XP * E - TECH SERIES Tonnage : 105T to 160T. Shot Weight (PS) : 72gms To 363gms. Screw Diameter (mm) : 25 to 50. Tie bar distance (mm) : 460 X 410 To 520 X 520. Mould Opening Stroke (mm) : 350 To 450. Servo Controlled High Speed ejection Ac Servo Motors For Energy Saving Suitable For Clean Room Application High Speed Ball Screw Driven 5 Point Twin Toggle Clamping Low Noise, Fast & Precise Moulding Compiled By Mathew Sebastian

5 MACHINE MAINTENANCE Screw Tip failure...causes and remedies Normally, when a machine is stopped, a layer of plastic material gets deposited between screw and the barrel surfaces. It cannot be fully avoided, even if the barrel is purged before stopping the machine. Hence, when the machine is restarted, even if the reading shows that the barrel has attained set temperature, what it really indicates is the body temperature of barrel and does not reflect the true condition of plastic material inside the barrel.. Auxiliary Equipment Focus BULK MATERIAL HANDLING SOLUTIONS PRESSURE FEED SYSTEMS Of late in India the trend is moving towards storage of plastic material in higher volumes using Silos. Falling in line with this trend, many plastic raw material suppliers are now coming out with either a 500 Kg or Jumbo Bag 1000 kg packing for bulk consumers. These developments necessitate a rugged system to handle large volumes of plastic raw material. At LTPML, we have now come out with a proven solution to address the above requirement of market, viz PRESSURE FEED SYSTEMS Based on the volume of material to be handled, there are options of selecting a 5 Tons/Hr Or 10 Tons/Hr handling systems for loading number of Silos in a plastics processing plant. When using Injection Molding Machine, many times we face problem of screw tip failure. While most of the time this failure could be attributed to barrel temperature, there are other factors which are conveniently over looked. On an analysis, it was found that majority of screw tip failures were reported at the time of machine start up after a long switch- off (week end) or brief switch-off (Moldchange, Materialchange etc.). Normally such screw tip failures are due to insufficient or no Cold start protection. What is Cold start protection? How to avoid such failures? In a barrel assembly, temperatures are measured by thermocouples inserted onto barrel. These thermocouples measure only barrel outer temperature. Hence even if the temperature shows correct reading, it does not guarantee softening of the plastic material inside the barrel, as plastic is a good insulator and hence does not fully absorb all the heat. MACHINE APPLICATION Process parameters Optimisation..a few tips It is quite possible that all heat has not penetrated inside the barrel, since some amount of time is required for heat transfer to take place to the center of barrel to melt the core of residual plastics. Under this condition if screw is moved for injection or refilling, the cold material at the front end of screw and also over the screw might hold the screw tip thereby breaking it. To avoid such failures, at the startup of production, barrel needs to be soaked sufficiently at operating temperature for a few minutes. It allows the heat to penetrate into the barrel and soften plastic material.this is called Cold start Protection. Normally, cold start protection time varies with the size of screw and type of material processed earlier and can range from 2 minutes to 15 minutes. Other possible reasons for screw tip failures are as below: Operating the material at low barrel temperature Heater failure, Poor alignment Foreign/metal parts in granules Non uniform pellet/grinding size - C.Somaskandan General Concept Model: A typical Pressure Feed System: Debagging Station Rotary Airlock Feeder Target Box Silo Conveying Line Bin Vent 1. When optimising process parameters, it is important to change not more than one parameter at a time until the effect of changed parameter on the quality of the moulding is clearly understood. There are often obvious changes which can be made where parameter influence becomes immediately apparent. 2. Optimisation should always begin with the quality of the moulding in mind. The fundamental link between quality characteristics and setting parameters are sufficiently well known. It is important to make a firm assessment of quality characteristics and their limits. Then the stability and quality of the process should be optimised on the basis of parameter and flow distribution. Only when this has been done can cycle time be optimised. 3. It has been observed in many injection moulding processes, that dosing gets completed well ahead of cooling time and hence pump runs in idle mode. This results in excess consumption of energy as compared to a process where in the dosing gets completed within very close proximity to lapse of cooling time.hence it is recommended to prolong dosing closer to cooling time, if process permits, to save energy. -S.Arun Kumar Pressure feed system for 5 Ton / hr comprising of Blower station with PLC Control, Rotary air lock valve, line injector, target box, bin vent filter, debagging station 600 liters and set of pipes and bends to have the pressure feed system connected to One 10 Ton Silo. The unit can remain common for number of Silos and can be filled one by one depending on the stock levels & procurement pattern. - R.Srinivasamoorthy Positive Displacement pressure Blower For more details, mail us at: moorthyr@larsentoubro.com

6 New Developments SECTOR ALLOCATION OF CFF Compact flash disc consists of 50 sectors. Each sector has same space as that of a floppy disc (1.44 MB). First 39 sectors are free and can be used for storing mould catalogues. Around 1900 mould catalogues can be stored in a single compact flash, whereas a floppy disc can store only about 50 catalogs. A backup of the compact flash can also be taken and stored in a PC. The last 10 sectors are reserved and it is not recommended to store mould catalogues in these sectors. Originality is a Virtue Compact Flash Floppy drive (CFF) for Ergocontrol This useful item is priced US$ 350 (Rs.15,500) apiece Ex-works. You can place your order by informing us your machine serial no. Part number of CFF is KP We will be holding the above price valid up to 31st Dec As you know, Ergocontrol has a floppy drive which is used for storing mould catalogues as well as for booting. Floppy discs and floppy drives are not rugged and hence are prone to failures. To overcome this and in keeping with new technologies, Compact Flash Floppy drive has been developed at LTPML. About CFF Always Buy Original Parts CFF drive is compatible with the existing floppy drive. Since compact flash is used instead of floppy disc life and reliability are enhanced. Compact flash has a higher memory storing capacity than a floppy disc, thereby in a single compact flash all the boot files (files required for ergocontrol) and mould catalogue can be stored. It is smaller in size. Please contact us at Spare LNTPPM@larsentoubro.com Phone From or ITS APPROVED STOCKISTS - G.Subramanian & N.Vijayakumar ENHANCE LIFE OF YOUR MACHINE WITH ORIGINAL PARTS