Powder rolling, also called roll compacting, is the important process to produce
metal strips. In powder rolling metal powder is fed from a hopper into
gap of a rolling mill and emerges from the gap as a continuous compacted
green strip. The rolls of the mill may be arranged vertically or horizontally.
The latter type of arrangement is more common, with either saturated feed
or starved feed.
The powder characteristics have the following effect on powder rolling:
Particle Shape: The generation of maximum ‘green’ strip strength to
withstand the rigours of handling through the process line require the particle
shape to be very irregular.
Compressibility: Good compressibility is required to ensure that sufficient
particle interlocking takes place to give adequate ‘green’ strip strength.
Good green strip has a density of at least 80/85 % theoretical. Compressibility is also of importance in determining the limiting dimensions of the roll compaction
mill.
Particle Size: The thickness of the finished strip and particle segregation
severely restricts the maximum particle size which can be tolerated in
the powder feed to the compaction mill.
Flowability: The powder must flow smoothly and quickly through hopper
systems with minimum tendency to stick slip or bridging.
Surface Oxidation: This plays a significant part in determining subsequent
powder behaviour.
The roll compaction operation can be divided into three distinct zones
(Fig.5.17):
1. The free zone where blended powder in the hopper is transported freely
downward under gravity. Here all the usual criteria of hopper flow apply.
2. The feed zone where the powder is being dragged by the roll surface
into the mill bite, but has not yet attained coherence.
3. The compaction zone close to the roll nip, where the powder becomes
coherent, the density changes rapidly and air has to be expelled.
In contrast to conventional rolling, the thickness of the strip can be rolled
in powder rolling is closely limited by the diameter of the rolling mill rolls.
The change in density is accomplished as the powder is transported through
the feed zone and the compacting zone. The length of these zones is determined
by the diameter of the rolls (D), the internal friction between the
powder particles and the friction between powder and rolls. With the geometry
shown in Figure 5.17, the nip angle α may be defined as
In addition to using powder rolling for the large scale production of strip
and sheet of base metal and alloys, the technique has also been employed
for a number of speciality type strip materials, e.g. nickel and cobalt alloys
for electronic and magnetic applications, porous powder rolled strip,
in particular stainless steel strip for filters and nickel strip for electrodes
and also an aluminium alloy strip for bearing applications.
(POWDER METALLURGY TECHNOLOGY ,G. S. Upadhyaya p.63-65)
Powder rolling(old)
Metal powder is introduced between the rolls and compacted into a "green strip", which is subsequently sintered and subjected to further hot-working and/or cold working and annealing cycles. Advantages:
- Cut down the initial hot-ingot breakdown step.
- Economical - metal powder is cheaply produced during the extraction process.
- Minimise contamination in hot-rolling.
- Provide fine grain size with a minimum of preferred orientation.
Udomphol T., Rolling of Metals, p. 21
High-feed Milling (new better)
The HFM method takes advantage of small setting angles. This gives minimal radial- and
maximal axial cutting forces. Which reduces the risk for vibrations and stabilises machining.
In turn, this allows raised parameters for cutting even when machining with a large overhang.
Gains from High Feed Milling are more than just higher productivity. Tool life is prolonged. This cuts tool costs. The comprehensive HFM programme suits all kinds of applications. Which gives you
great fl exibility. Many of the cutter bodies are coated with hardy nickel chrome alloy prolonging both body and insert life.
High Feed Milling and long overhang co-operate in perfect harmony. Using long overhang with high feed cutters, you can machine three times faster.
This implies that your choice is trigon style inserts and cutting edges designed with very big radii. So the small depth of cut and high feed rates without vibration come naturally. And so do the
cutting forces, always in an axial direction. Actually, for most High Feed Milling operations trigon style
inserts are preferred over round. The reason is that the main cutting forces are located at the bottom of the cutting edge.
Of course, there are situations when you use square inserts – in such cases with a small setting angle. And mostly in High Feed heavy roughing applications using powerful machines in stable
conditions or in horizontal milling operations, making chip evacuation more effective.
But in vertical operations trigon style inserts are a safe choice, offering excellent chip evacuation. Also when it comes to smaller machines with high rpm.On top of this, the HFM process doesn’t demand increased
rotational speed from the machine.With insert grades that can machine difficult materials, the predictability of
the tools also increases. The result: fewer tool changes, less rejects, less reworking.
(SECO TOOLS, High Feed Milling brochure, p.4 )
High-feed Milling (March 26, 07:49) (old)
High-feed milling is a roughing technique that works with cutters and inserts designedspecifically for the technique. Inserts typically feature large sweeping radii and positive rakes. The high-feed method takes advantage of small setting angles (55° or less). This produces a minimal radial and a maximum axial cutting force. As a matter of fact, the cutting forces are directed towards the machine spindle in the axial direction. This is the stiffer direction of the machine, which reduces the risk for vibrations and stabilizes machining.
This allows for higher cutting parameters even when machining with a large overhang. Therefore, instead of cutting with greater depth, it does the opposite: it pairs shallow depth of cut with high feed per tooth, in some cases higher than 1.5 mm.
At the same time the axial depth of cut is very small, leading to a near-final shape in the case of complex surfaces. Consequently semi-finishing operation is eliminated. This greatly reduces the machining time in the case of moulds or dies.
(Davim J. P., Machining of hard materials, p. 76)
Collaborative Manufacturing (new better)
Collaborative manufacturing management (CMM) is formally defined as ‘the practice of
managing by controlling the key business and manufacturing processes of a manufacturing
enterprise in the context of its value networks’ (ARC Advisory Group – October 2001). It
builds on a collaborative infrastructure, business process management (BPM) services and
real-time strategic business management tools, together with critical applications,
production systems and enterprise information, to maximize the responsiveness, flexibility
and profitability of the manufacturing enterprise, together with the overall effectiveness of
the value networks. At a conceptual level CMM is a new model for business management
which shows the relationship between the real time and transaction paradigms of reality by
expanding the traditional two-dimensional model into a third dimension.
The CMM model has three dimensions or axes onto which the
systems can be mapped. The enterprise axis is the linear dimension where the system sits
in relation to the real-time/transaction distinction. The value chain axis defines the
position in the process that starts with the supplier’s supplier and ends with the
customer’s customer. The life cycle axis looks at the traditional product design-launchgrowth-
maturity-support continuum. The nodal sphere defines the areas of the business
and this sphere does not exist in a vacuum either as there are linkages to the outside
world, from every possible point on the surface of the sphere. The Internet, exchanges
and portals can be used to link the enterprise to the outside world.
‘The essence of collaboration is the ability for individual plants to synchronize their
work in real time based on accepted orders, and to coordinate the production and delivery
of component materials at the production level in a highly distributed manner’ (ARC –
October 2001).
The functions of CMM have been divided into seven areas.
-Synchronize business processes with manufacturing processes
-Optimize the supply-side value chain
-Generate value by empowering people and measuring results
-Implement collaborative design and engineering
-Link operations with customers
-Enable collaborative maintenance and manufacturing support
(Gerhard Greeff, Ranjan Ghoshal Practical E-Manufacturing and Supply Chain Management 2004 p.63-65)
Collaborative Manufacturing
CM is a very broad arena which incorporates many other topical themes of the day, including team design, computer-supported collaborative work, agile manufacturing, enterprise integration, virtual enterprises, high-performance distributed computing, concurrent engineering, computer-integrated manufacturing, virtual reality, global sourcing, and business process reengineering. In general, CM is defined by the following attributes:
• Integrated product and process development, including customers and suppliers;
• Flexible manufacturing distributed over networks of cooperating facilities;
• Teamwork among geographically and organizationally distributed units;
• High-technology support for the collaboration, including high-speed information networks and integration methodology;
• Multidisciplines and multiple objectives.
What is the payoff for CM? Companies that can engage effectively in CM will have the potential for
• Better market opportunities;
• A wider range of design and processing options over which to optimize;
• Fewer and looser constraints restricting their capabilities;
• Lower investment costs;
• Better utilization of resources;
• Faster response to changes.
( Frank Kreith, CRC Press Mechanical Engineering Handbook 1999, ch.13 pg.120)
Hierarchical Production Planning (new )
Hierarchical Production Planning is the division of the entire
production planning process, all the decisions to be made, into a
hierarchy of decisions to be made sequentially, with the results of the
higher-level decisions explicitly constraining the lower-level
decisions. The hierarchy is designed to fit the organizational structure
and to provide for ease of review at each managerial level. Higher-level
decisions have longer lead times, longer planning horizons, and are
concerned with aggregates (e.g., total manpower, total product line
demand) while the lowest-level decisions have shorter lead times, shorter
planning horizons, and are concerned with individual items, machines and
workers.
The overall planning process is divided, as nearly as possible, in a
way which makes the result of the sequential, hierarchical process nearly
as good as could have been obtained from a monolithic process which
treated all of the detail in making the most aggregate decisions.
There is a natural hierarchy of decisions ranging from strategic
planning choices through tactical planing to detailed or operational
planning and control. This hierarchy is based on the lead times to
execute decisions, the planning horizons to be considered in analyzing
and evaluating alternatives, and the magnitudes of the costs affected by
the decisions . The hierarchy is natural in the sense that long lead time
decisions necessarily constrain short lead-time decisions. For example,
the number of people in the v/orkforce is limited by the plant size and
the amount of equipment and can be changed (ordinarily) with a shorter
lead time than is required to change the plant facilities.. Also, the
cost differentials resulting from different plant size decisions tend to
be much larger than the cost differentials resulting from differences in
workforce size.
One of the consequences of these characteristics of the hierarchy of
production planning decisions is relative independence of decisions.
That is, high-level decisions can usually be made without taking into
account the way in which lower-level decisions will later be made. One
can use aggregate instead of detailed data in making aggregate decisions
and incur little, if any, cost penalty as a consequence of the
approximation.
(Harlan C. Meal , Hierarchical Production Planning , p12 )
Hierarchical Production Planning (old)
Hierarchical production planning (HPP) represents an approach and a philosophy towards the organization, planning and scheduling of production activities which has existed both in theory and practice fr several decades. Originally developed as a planning and scheduling approach primarily for production activities, the philosophy of hierarchical production planning has evolved to encompass a broad range of supply chain management activities. Today, one can observe what can broadly be viewed as extensions of the HPP philosophy across activities ranging from production planning and integrated distribution and production planning to supply chain wide inventory management, transportation and warehouse planning and scheduling,sales and marketing planning and so on. In many of these activity areas, understandably no mention or acknowledgement of the hierarchical production planning approach exists. Nevertheless, upon closer inspection, clear similarities in techniques and philosophy exist among the myriad decision-making approaches used today to manage the diverse aspects of the supply chain and those techniques and approaches which embody hierarchical production planning. The common theme of a hierarchical approach towards the management of decision-making activities across the supply chain suggests that there exist benefits and broad learnings to be gained from exploring the hierarchical approaches and techniques utilized today in managing different components of the supply chain.
(Hierarchical Operations and Supply Chain Planning, Tan C. Miller,p.1)
Impregnation (Better)
Impregnation is the term used when oil or other fluid is permeated into the pores of a
sintered PM (powder metallurgy) part. The most common products of this process are oil-impregnated bearings, gears, and similar machinery components.Self-lubricating bearings, usually made of bronze or
iron with 10% to 30% oil by volume,are widely used in the automotive industry.The treatment
is accomplished by immersing the sintered parts in a bath of hot oil.
An alternative application of impregnation involves PM parts that must be made
pressure tight or impervious to fluids. In this case, the parts are impregnated with various
types of polymer resins that seep into the pore spaces in liquid form and then solidify. In
some cases, resin impregnation is used to facilitate subsequent processing, for example, to
permit the use of processing solutions (such as plating chemicals) that would otherwise
soak into the pores and degrade the product, or to improve machinability of the PM
workpart.
(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems 4thEdition, pp. 357)
Impregnation (old)
The vast majority of catalysts are prepared by Impregnation of the active metals on the compacted support. The metal-containing solutions and cosolutions are typically highly concentrated and stabilized by a diverse range of inorganic, as well as organic, additives. The Impregnation solution must be completely clear and stable on storage/transportation. The solution viscosity should also not be too high to prevent difficulties in the Impregnation process. Phosphoric acid, ammonia and H2O2 are amond the most frequently used inorganic additivies, if we give a example.
Krijn Pieter de Jong, Synthesis of solid catalysts, 2009, page 309)
This comment has been removed by the author.
ReplyDelete