Sleeve Effectiveness to increase Yield. A casting simulation based study.

Introduction:

Insulating or exothermic sleeves are used to increase the yield in foundry practice. Each of the sleeve manufacturer provides a large variety of sleeves in different sizes. Function of sleeve is predominantly to enhance the effective casting modulus by increasing feeding efficiency. This is represented by a modulus extension factor (MEF). Details studying the effectiveness of feeding aids are given in IS 15865:2009 and such similar standards.

A methoding / gating designer has to decide for a given casting application

  1. which is the best type of sleeve?
  2. where the sleeves have to be located?
  3. how many such sleeves needed?

Often, new entrants into the casting process design, who lack experience and knowledge, are faced with a difficulty of making the appropriate choices of sleeve to increase yield in casting. There will be problems to evaluate the feed safety margins, volumetric feed efficiency of various sleeves to make the right choice. Casting simulation software can help in making such decisions. Further casting simulations help to make the decisions faster, and with more accurate data. Such information coming out of casting simulation will be very useful even for experienced methods developer.   Simulations can help to reduce the feed safety margin and use simulation to develop process control parameters.

Authors demonstrate the usage of a casting simulation software ADSTEFAN for studying the effectiveness of sleeves and demonstrate how yield improvement can be enhanced. To demonstrate the concept a simple casting of a cube is taken for analysis.   Five cases of different sleeves are considered for demonstration sleeve effect on shrinkage porosity formation.

  1. Without any sleeve (sand riser)
  2. With insulating sleeve (Insulation sleeve)
  3. With exothermic sleeve (ZP 8/11 K Foseco Kalminex 2000plus sleeve)
  4. With exothermic sleeve (ZP 8/14 K Foseco Kalminex 2000plus sleeve)
  5. With exothermic sleeve (ZP 5/11 K Foseco Kalminex 2000plus sleeve)

Figures 1a to 1e represent these cases for different sleeves used.

1a
Fig. 1: Sleeve arrangement for various cases

Casting Simulation to study the effectiveness of sleeves

Authors use a commercially available ADSTEFAN (developed by Prof Niyama of Japan). All cases are considered for material 0.4% C_ Steel and pouring temperature1560 C. Results of solidification and shrinkage porosity formation are given in Figure 2a to 2e. Figure 2 shows the height of the porosity area, including the additional height of the riser considering the factor of safety/ safety margin (conventionally taken as 80% of the riser diameter).   In the figure, the red regions show the regions of shrinkage porosity. Blue represents the fully solidified metal region.

2
Fig. 2: Degree of Soundness and Shrinkage porosity for cube

Correlation of simulation with physical casting:

Many of the users of casting simulation software complain about the lack of good correlation between simulation and plant data. In foundries such deviations between plant production and simulation software are seen mainly due to:

  • Improper inputs to the software
  • Lack of proper training for using simulation software,
  • Inadequacy of the simulation software

If these issues are addressed, quite a good correlation can be achieved by casting simulation results and plant observation of casting defects. Figure 3 shows comparison of physical castings with the corresponding ADSTEFAN casting simulation results. In left side of figure 3, the defect is penetrating deep into the product. In the figure in middle, the shrinkage has just penetrated casting and is still risky. In the right figure, the casting does not have any defect. These 3 case, demonstrate good correlation between simulation using ADSTEFAN and physical castings.

4
Fig.4: Comparison of Degree of Soundness in castings produced and simulated. Good correlation with the ADSTEFAN casting simulation and cast part is seen.

Results: Simulating Effectiveness of Sleeves

Table-1 shows the calculation of yield for all the 5 cases. In the case-1, a sand sleeve is used and obviously the casting yield is the lowest at 30%. In case-2, a normal insulating type sleeve is used, and the yield increases to 55%. Yield will increase to 25 % when we use a casting sleeve of type insulating sleeve.

Case-4 shows the usage of an exothermic sleeve which has a higher MEF compared to case-3. As a result, as seen in figure 2, no shrinkage porosity is formed. However, for this casting such a sleeve is an over kill and the yield is reduced.

Case-5 shows the usage of an exothermic sleeve which has lower MEF compared to case-3. As a result, as seen in figure 2, a shrinkage defect is formed there is no margin of safety available. It will be risky to produce the castings with this sleeve.

Table-1:   Effectiveness of sleeve for yield improvement.

Case Sleeve type Sleeve height Porosity height Safety Margin Height Yield % Remarks
Case-1 Sand Riser 147 75 30
Case-2 Insulation sleeve 128 111 29 55
Case-3 Exothermic sleeve (ZP 8/11 K) 109 69.5 27 78.18 Best Optimised Sleeve
Case-4 Exothermic sleeve (ZP 8/14 K) 138 78 72 62.58 Good. But not best optimised
Case-5 Exothermic sleeve (ZP 5/11 K) 110 159 67.77 Shrinkage formed

Conclusion:

Casting simulation results (using ADSTEFAN software) have been shown to be correlating well with the physical castings produced. From the casting simulation results, it is seen that for casting of a cube, sleeve ZP 8/11 K (or equivalent) is the best and optimum. For each casting component, using simulations, best sleeve choice can be determined, for that material, shape, and process conditions. If the process can be tightly controlled, simulation gives clues on how much the feed safety margin can be reduced, to increase yield further.

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How weight of a long member was reduced??!!

Introduction to Hydroforming:

Hydroforming is a metal fabricating and forming process which allows the shaping of metals such as steel, stainless steel, copper, aluminum, and brass. This process is a cost-effective and specialized type of die molding that utilizes highly pressurized fluid to form metal.

Hydroforming Animation
Hydroforming Animation

In tube hydroforming (THF) there are two major practices: high pressure and low pressure. With the high pressure process the tube is fully enclosed in a die prior to pressurization of the tube. In low pressure the tube is slightly pressurized to a fixed volume during the closing of the die (this used to be called the Variform process).

Today it is mostly used in the automotive sector, where many industrial applications can be found. It is also a method of choice for several tubular members of bicycles. 

THF is a method in which tubes are formed by placing a tube between a pair of metal dies and applying hydraulic pressure to inside of tube. In order to prevent wall thinning of tube, it is forced towards and into the dies from both its ends (called axial feeding). Internal pressure and tube end feeding are two important parameters in hydroforming process. The quality of hydroforming depends largely on these parameters and their interactions. Non-optimized choice of these parameters can lead to unacceptable wall thinning (even tube bursting) or wrinkles in final part.

Tube hydroforming has attracted increased attention in automobile industry recently because the automobile designers continue to look for better solutions to reduce weight and cost of vehicle.

The problem??

The proposed hydroforming component to be developed was of a high dual phase high strength steel DP 340/590. It replaced a long member which was produced by conventional stamping and welding of ‘C’ sections made out of conventional carbon steels.

Long member
Long member
Tool setup
Tool setup

Model description and analysis details:

Single piece/member is not a feasible option for the hydro forming, based on large capital cost involved and due to large tonnage required to form 4mt single piece component, as compared to multi piece options. For multi piece, selecting the joining location is a challenge. Based on the perimeter expansion analysis, four piece options has been decided as discussed in the figure below, the locations were chosen based on bracket location.

Execution and Exploaration:

During the entire exercise of the hydro forming, lot of things were explored.

  • We were able to understand how important it is to choose the location in order to optimize the weight of the component.
  • During hydro forming simulation, it was observed that friction (lubrication) plays a significant role in hydro forming.
  • Larger the friction co-efficient, thinning of the material was observed.
  • In the same way, study was done to understand the effect of hardening parameter, it was clearly indicative that, higher the hardening co-efficient, lesser is the thinning.
  • The major exploration was, the effect of loading path (Pressure time and Axial feed time curve). Since pressure sequencing depends on tube diameter, thickness, material ultimate strength and minimum radius of the die, any one parameter will alter the loading path of hydro forming.
Expansion Curves
Expansion Curves

Conclusion:

With hydroforming approach, the overall weight saving of the component is 11.4% without any design changes to the component. Weight reduction could have further been improved if some design changes are allowed.

dfwfwee
Effective strain distribution after hydroforming
Thickness distribution along tube length
Thickness distribution along tube length
Forming limit diagram
Forming limit diagram

How weight of an SUV door was reduced??!!

Introduction to Hydroforming:

Hydroforming is a metal fabricating and forming process which allows the shaping of metals such as steel, stainless steel, copper, aluminum, and brass. This process is a cost-effective and specialized type of die molding that utilizes highly pressurized fluid to form metal.

Hydroforming Animation
Hydroforming Animation

In tube hydroforming (THF) there are two major practices: high pressure and low pressure. With the high pressure process the tube is fully enclosed in a die prior to pressurization of the tube. In low pressure the tube is slightly pressurized to a fixed volume during the closing of the die (this used to be called the Variform process).

Today it is mostly used in the automotive sector, where many industrial applications can be found. It is also a method of choice for several tubular members of bicycles. 

THF is a method in which tubes are formed by placing a tube between a pair of metal dies and applying hydraulic pressure to inside of tube. In order to prevent wall thinning of tube, it is forced towards and into the dies from both its ends (called axial feeding). Internal pressure and tube end feeding are two important parameters in hydroforming process. The quality of hydroforming depends largely on these parameters and their interactions. Non-optimized choice of these parameters can lead to unacceptable wall thinning (even tube bursting) or wrinkles in final part.

Tube hydroforming has attracted increased attention in automobile industry recently because the automobile designers continue to look for better solutions to reduce weight and cost of vehicle.

The problem??

The proposed hydroforming component to be developed was of a high dual phase high strength steel DP 340/590. It replaced a long member which was produced by conventional stamping and welding of ‘C’ sections made out of conventional carbon steels.

Long member
Long member
Tool setup
Tool setup

Model description and analysis details:

Single piece/member is not a feasible option for the hydro forming, based on large capital cost involved and due to large tonnage required to form 4mt single piece component, as compared to multi piece options. For multi piece, selecting the joining location is a challenge. Based on the perimeter expansion analysis, four piece options has been decided as discussed in the figure below, the locations were chosen based on bracket location.

Execution and Exploaration:

During the entire exercise of the hydro forming, lot of things were explored.

  • We were able to understand how important it is to choose the location in order to optimize the weight of the component.
  • During hydro forming simulation, it was observed that friction (lubrication) plays a significant role in hydro forming.
  • Larger the friction co-efficient, thinning of the material was observed.
  • In the same way, study was done to understand the effect of hardening parameter, it was clearly indicative that, higher the hardening co-efficient, lesser is the thinning.
  • The major exploration was, the effect of loading path (Pressure time and Axial feed time curve). Since pressure sequencing depends on tube diameter, thickness, material ultimate strength and minimum radius of the die, any one parameter will alter the loading path of hydro forming.
Expansion Curves
Expansion Curves

Conclusion:

With hydroforming approach, the overall weight saving of the component is 11.4% without any design changes to the component. Weight reduction could have further been improved if some design changes are allowed.

dfwfwee
Effective strain distribution after hydroforming
Thickness distribution along tube length
Thickness distribution along tube length
Forming limit diagram
Forming limit diagram

Finite Element Analysis of Frame Structure

This analysis was to a client company, which is an OEM of Frames. The needs were to create an FE model for performing static analysis of the frame structure and to perform the Fatigue Life Assessment of the welded location in the structure.

4

Pic: Nominal stress contour plot of the frame

The key complexities faced by our engineers were while performing the fatigue life assessment as when the word ‘life-assessment’ comes, yes, there will be complexities!

Creating a fine FE sub-model was a challenge by itself. Identifying the hot spot [1] location of the weld was another challenging task, which indeed needed hours of peaceful research. The greatest challenge was faced when performing the extraction of high nominal stress of the hot spot location, in order to perform the fatigue life assessment of the weld location.

3Pic: Sub model of the weld spot

Was it overcome?  

Yeah! By running the sub-modelling [2] analysis for the weld location.

Coming to the solution, we applied the Boundary conditions, loading and stress results from the global model to the sub model. The maximum stresses were observed at the root of weld. Membrane stress and the bending stress values were extracted at the weld root region to obtain the nominal stress values for the same region. Fatigue life assessment was done by using the nominal stress value extracted at the weld root.

2Pic: Sub model Boundary condition

The customer in turn saved a lot of experimental cost by simulating it prior to experimentation as it would have taken days together. Also, a large chunk of the cost, time and material were reduced to a great extent. There will always be induced errors during testing, some due to variation in the manpower and testing induced errors. Such errors were also predicted and reduced.

1Pic: Stress contour model of the sub model

[1] Hot spot- region/zone where the temperature is high(exceeding the limit).

[2] Sub modeling is a finite element technique used to get more accurate results in a region of your model. Often in finite element analysis, the finite element mesh may be too coarse to produce satisfactory results in a region of interest, such as a stress concentration region in a stress analysis. The results away from this region, however, may be adequate.

To obtain more accurate results in such a region, you have two options: (a) reanalyze the entire model with greater mesh refinement, or (b) generate an independent, more finely meshed model of only the region of interest and analyze it. Obviously, option (a) can be time-consuming and costly (depending on the size of the overall model). Option (b) is the sub modeling technique.